Microlithographic projection exposure apparatus

ABSTRACT

A projection exposure apparatus for microlithography comprises illumination optics for illuminating object field points of an object field in an object plane is disclosed. The illumination optics have, for each object field point of the object field, an exit pupil associated with the object point, where sin(γ) is a greatest marginal angle value of the exit pupil. The illumination optics include a multi-mirror array that includes a plurality of mirrors to adjust an intensity distribution in exit pupils associated to the object field points. The illumination optics further contain at least one optical system to temporally stabilize the illumination of the multi-mirror array so that, for each object field point, the intensity distribution in the associated exit pupil deviates from a second adjusted intensity distribution in the associated exit pupil by less than 0.1 in at least one of an inner σ or an outer σ.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims benefit under 35 USC120 to, U.S. application Ser. No. 12/818,844, filed Jun. 18, 2010, whichis a continuation of, and claims benefit under 35 USC 120 to,international application PCT/EP2008/010801, filed Dec. 18, 2008, whichclaims benefit of German Application No. 10 2008 008 019.5, filed Feb.7, 2008 and U.S. Ser. No. 61/015,918, filed Dec. 21, 2007. U.S.application Ser. No. 12/818,844 and international applicationPCT/EP2008/010801 are hereby incorporated by reference in theirentirety.

FIELD

The disclosure relates to microlithographic exposure apparatus thatimage a mask onto a light sensitive surface, including such apparatusthat include illumination optics that contain an array of mirrors.

BACKGROUND

Microlithographic projection exposure apparatus often includeillumination optics for producing an intensity distribution in an exitpupil associated with object field points in an object field which isilluminated by illumination optics. Such apparatus are known, forexample, from U.S. Pat. No. 6,285,443 B1. The structuring (i.e.producing a desired intensity distribution) of exit pupils results fromstructuring an intensity distribution in angle space, which is producedby a diffractive optical element (DOE) in a plane which is Fourierrelated by Fourier optics to a subsequent pupil plane. In the exit pupilthe intensity distribution is described as a function of pupilcoordinates which correspond to angles in the plane of the DOE. Variablezoom objectives and/or axicon systems, which are arranged between theDOE and the pupil plane, may be used to selectively vary the angledistribution produced by the DOE. It is thereby possible, for example,to adjust the coherence of the illumination, for example the outerand/or inner σ of a setting, with σ being the coherence parameter whichwill be described in more detail below. These adjustable elements makeit possible to obtain a more complex structuring of exit pupils. Thezoom objective and/or the axicon system can ensure a radially symmetricor axisymmetric redistribution of light about the optical axis of thepupil plane as a symmetry axis. Without restriction of generality,symmetry of the axicon is assumed with respect to the optical axis.

For the coherence parameters indicated above, the outer σ is a measureof the fill factor of light in the exit pupil. Conversely, the inner σis a measure of the fill factor of central obscuration or shadowinginside the light-filled region in the exit pupil that is described bythe outer a. At least one further set of Fourier optics transforms thedistribution as a function of the pupil position in the pupil plane intoan angle distribution in a subsequent object plane, so that the exitpupils of the object field points of the object field in the objectplane of the illumination optics are structured.

A restricting factor in these projection exposure apparatus can be thatstructuring produced by a DOE can be modified only to a small extent,essentially radially symmetrically or axisymmetrically with respect tothe optical axis, by adjusting lenses of the zoom objective or elementsof the axicon system. If a completely different structure of the exitpupil is desired, it is desirable to change the DOE. In practice, thetime taken to provide a suitable DOE for the desired pupil structuringmay be several days or even weeks. Such projection exposure apparatusare therefore only limitedly suitable for fulfilling the customer'sdesired rapid change. For example, it is not possible to a changebetween very different structurings of the exit pupils within fractionsof a second.

Projection exposure apparatus for microlithography, having illuminationoptics for rapidly changing the structuring of exit pupils viamulti-mirror arrays (MMA) are known, for example, from WO 2005/026843A2.

Methods for calculating optimal structurings of exit pupils ofillumination optics of a projection exposure apparatus as a function ofmask structures to be imaged on the reticle are known, for example, fromU.S. Pat. No. 6,563,566 B2 and US 2004/0265707 A1.

SUMMARY

In some embodiments, the disclosure provides a projection exposureapparatus having a multi-mirror array (MMA) for rapidly and reproduciblychanging the structuring of exit pupils of object field points ofillumination optics of a projection exposure apparatus.

In certain embodiments, a projection exposure apparatus formicrolithography contains at least one optical system for temporallystabilising illumination of the multi-mirror array (MMA) so that, foreach object field point, the intensity distribution in the associatedexit pupil deviates from a desired intensity distribution in theassociated exit pupil as follows:

-   -   in the case of a centroid angle value sin(β), by less than two        percent expressed in terms of the greatest marginal angle value        sin(γ) of the associated exit pupil and/or;    -   in the case of ellipticity, by less than two percent; and/or    -   in the case of a pole balance, by less than two percent.

The inventors have discovered that the DOE in conventional projectionexposure apparatus, as described for example in U.S. Pat. No. 6,285,443B1, can lead to strong light mixing in the exit pupils. Here, stronglight mixing means that the intensity of a region in the exit pupil isformed by the superposition of a multiplicity of illumination rays,which come from essentially all positions or field points of the DOE. Insuch systems the temporal and/or spatial fluctuations of the lightsource, for example spatial laser jitter, are therefore balanced out bythe strong light mixing of the DOE. During the exposure process, thisgives approximately temporally stabilised structuring in the exitpupils, which fluctuates only to a small extent relative totime-averaged structuring. For conventional projection exposureapparatus with DOEs, it is now possible in a wide variety of ways tomake such time-averaged structuring in the exit pupils approximatestructuring desired for the exposure process. Estimates, which areapplicable for a large number of systems, have revealed that about80,000 or more mirrors of a multi-mirror array (MMA) for a projectionexposure apparatus are useful to replicate the light mixing property ofa DOE of a conventional projection exposure apparatus. Such multi-mirrorarrays (MMA) with so large a number of mirrors for projection exposureapparatus, to generate strong light mixing, are currently not believedto be technologically achievable.

According to the disclosure, it has been discovered that for projectionexposure apparatus having fewer than 80,000 mirrors, temporalstabilisation of the illumination of a multi-mirror array (MMA) givessimilarly good or even better time-averaged structurings of the exitpupils. Structuring of exit pupils of the projection exposure apparatus,calculated as optimal and desired by the user of the projection exposureapparatus, is therefore reproducible with high accuracy by theprojection exposure apparatus during the exposure process. Fluctuationsin the structuring of exit pupils with only very small tolerabledeviations relative to the desired structuring are therefore achievable.This means that systems disclosed herein can advantageously allow thelight mixing property of a DOE in the pupil to be replicated fortemporally stabilising desired structuring of an exit pupil. The exitpupil is therefore advantageously decoupled from the temporal and/orspatial fluctuations of the light source, for example laser jitter of anexcimer laser, by temporally stabilising the illumination in a positionor field plane of the illumination optics, which contains, for example,the MMA with fewer than 80,000 mirrors.

The structuring of an exit pupil is equivalent in meaning here to anintensity distribution in the exit pupil. In the specialist'sterminology, setting is also referred to instead of structuring of anexit pupil.

The exit pupil of an object field point is defined in optics textbooksas the image of the aperture-limited stop, which results from imagingthis stop through the optics following the stop in image space.Expressed another way, the exit pupil is the image of theaperture-limited stop as it appears with backward observation of thestop as seen from the object field point through the optics followingthe stop. If the aperture-limited stop lies at a distance from thesubsequent optics shorter than the value of the focal length of thesubsequent optics, then the exit pupil is a virtual image of theaperture-limited stop and precedes the object plane of the object fieldpoint in question in the light direction. But if the stop lies at adistance from the subsequent optics longer than the value of the focallength of these optics, then the exit pupil is a real image of theaperture-limited stop which may for example be captured or representedby a screen at the position of the exit pupil. In a telecentric system,the aperture-limited stop lies at a distance from the subsequent opticswhich corresponds to the focal length of the subsequent optics, so thatthe exit pupil is found both as a virtual image of the aperture-limitedstop at infinity in the light direction before the object field plane ofthe object field point in question, and as a real image of theaperture-limited stop in the light direction at infinity after theobject field plane of the object field point in question. This virtualor real image of the aperture-limited stop as the exit pupil of atelecentric system may readily be obtained by those illumination rays ofthe object field point which can just still pass through theaperture-limited stop (marginal rays) at the object field point beingextended in a straight line backwards or in a straight line forwards toinfinity. A position of an illumination ray in the virtual or real imageof the aperture-limited stop as the exit pupil of an object field pointin this case corresponds to the associated angle of the illumination rayin the object plane at the object field point. The correspondence ismade here using the tangent of the angle of the illumination ray, whichat the same time is the ratio of the distance of the position of theillumination ray in the exit pupil from the exit pupil centre to theexit pupil distance from the object field plane. Since this involves aone-to-one correspondence between distances of positions in the exitpupil relative to the centre of the exit pupil and the angle in theobject field plane via the tangent function, an alternative definitionof the exit pupil using the angles in the object field plane is to betaken as valid in the scope of this application in addition to theclassical definition of the exit pupil in optics textbooks. The exitpupil of an object field point in the scope of this application is theangle range or angle space of the object field point in the objectplane, which is limited by the aperture-limited stop of the illuminationoptics and within which the object field point can receive light fromthe illumination optics. This definition of the exit pupil in the scopeof this application has the advantage that the angle range or anglespace of the object field point in the object plane, within which theobject field point can receive light from the illumination optics, ismore readily accessible for technical measurement purposes than thevirtual or real image of the aperture-limited stop at infinity.

As an alternative, instead of in the form of an angle range or an anglespace in the object plane, the exit pupil may also be described as aFourier transform thereof in the form of a pupil plane of so-calledFourier optics. Such Fourier optics could for example be part of ameasuring instrument for analysing exit pupils, which is introduced intothe object plane of the illumination optics. By the Fourier relationbetween the object and pupil planes of the Fourier optics, a height of apoint of the pupil plane of the Fourier optics measured against theoptical axis in the pupil plane is thereby associated with a sine of anillumination angle measured against the optical axis in the objectplane.

The structuring of an exit pupil, or equivalently the intensitydistribution in an exit pupil, may therefore be described either as anintensity distribution over the image plane of the virtual or real imageof the aperture-limited stop, or as an intensity distribution over thesurface in a pupil plane of Fourier optics, or as an intensitydistribution over angle ranges or over the angle space in aposition/image or field plane.

In general, illumination optics for a projection exposure apparatus formicrolithography have a telecentric beam path in the object or reticleplane with less than 50 mrad deviation from the telecentricitycondition. Such an approximation to a telecentric beam path in thereticle plane is advantageous for the tolerances with which the reticleis desirably positioned along the optical axis for optimal imaging. Inperfect telecentric illumination optics with telecentricity values of 0mrad, the virtual or real images of the aperture-limited stop as exitpupils of the illumination system lie at infinity, and the exit pupilsof all field points therefore coincide with one another. The angleranges of the object field points as exit pupils in the scope of thisapplication, in which the object field points can receive light from theillumination optics, likewise coincide.

With a small telecentricity profile of less than 50 mrad over the objectfield in the object or reticle plane, the virtual or real images of theaperture-limited stop as exit pupils are mutually decentered at a verylarge distance from the illumination optics. Moreover, the angle rangesof the object field points as exit pupils in the scope of thisapplication are mutually tilted in the object plane. For this reason,and for the reason that other imaging errors of the illumination opticsmay lead to further differences in the exit pupils of the object fieldpoints, a general exit pupil of illumination optics for a projectionexposure apparatus will not be considered in the scope of thisapplication, rather distinction will be made according to the individualexit pupils of the object field points and the respective intensitydistribution in the individual exit pupils of the object field points.In the ideal case, as already mentioned, these exit pupils may alsocoincide.

In the pupil planes of Fourier optics or Fourier planes conjugatedtherewith, for example in the pupil planes inside illumination optics orin the pupil planes of measuring optics for analysing pupils, it ispossible either to influence an intensity distribution in the relevantplane or measure it there. In this case, these planes need notnecessarily be planes in the sense of the word “planar”, rather they mayalso be curved in up to two spatial directions. It is likewise possiblein the object/image or field planes, or Fourier planes conjugatedtherewith, either to influence an intensity distribution over the anglesin the relevant plane or measure it there. Here again, thegeneralisation mentioned for the pupil planes applies to the term“plane”.

As a measure of a deviation of a desired intensity distribution from anintensity distribution of an exit pupil of an object field point,produced in a projection exposure apparatus, inter alia it is feasibleto use the difference of the centroid angle value sin(β) of the twointensity distributions relative to the greatest marginal angle valuesin(γ) of the associated exit pupil. Angle values in the scope of thisapplication are intended to mean the sine, sin(x), of the correspondingangle x. The marginal angle value is therefore intended to mean the sineof the angle at which a marginal point of the exit pupil is seen fromthe object field point with respect to the optical axis or an axisparallel thereto. With the alternative definition of the exit pupil asan angle range of an object field point, within which the object fieldpoint can receive light from the illumination optics, the marginal anglevalue is the sine of a marginal or limiting angle of the angle rangewhich applies as an exit pupil here. The greatest marginal angle valuesin(γ) is the greatest-magnitude angle value of all marginal angles ofall marginal points of the exit pupil, or the greatest-magnitude anglevalue of all marginal angles of the angle range which applies as an exitpupil here. The centroid angle value sin(β) is the sine of the centroidangle β of an intensity distribution in the exit pupil, and this in turnis the angle of the direction in which the centroid of the intensitydistribution in the exit pupil is perceived from an object field point.

The direction, in which the centroid of the intensity distribution inthe exit pupil is perceived, is often also referred to as the centralray direction. The centroid angle value, or the sine of the central rayangle, is at the same time the measure of the telecentricity of the exitpupil for a given intensity distribution.

In the case of telecentricity, distinction is often also made betweengeometrical and energetic telecentricity (see below). In the case ofgeometrical telecentricity, furthermore, distinction is made between theprincipal ray telecentricity (see below) and the geometricaltelecentricity with uniform rotationally symmetric filling of the exitpupil. The latter is equivalent in meaning to the centroid angle value,or the sine of the central ray angle, in the case of uniformrotationally symmetric filling of the exit pupil with light up to alimiting angle value, which can vary between zero and the greatestmarginal angle value.

With essentially uniform rotationally symmetric filling of the exitpupil with light, i.e. an essentially uniform rotationally symmetricintensity distribution in the exit pupil, so-called σ settings orpartially coherent settings are also referred to. In the specialist'sliterature, the outer σ of a setting is intended to mean the ratio ofthe sine of that angle to the sine of the greatest marginal angle, atwhich the light-filled region in the exit pupil ends abruptly. With thisdefinition of the outer σ of a setting, however, the conditions in realillumination optics are neglected, such as the existence of imagingerrors, ghost images and scattered light. An abrupt transition of brightand dark regions in the exit pupil can be produced only approximately byusing stops in a pupil plane of the illumination optics, since theimaging errors, the ghost images and the scattered light can then forthe most part be neglected. The use of stops in the pupil planes of theillumination optics to produce settings, however, can lead to lightlosses and therefore to a reduction in the throughput of substrates orwafers to be exposed. In the scope of this application, the definitionof the outer σ of a setting is to apply only for illumination optics forprojection exposure apparatus which produce a desired setting via stops.For all other illumination optics, contrary to the textbook definitionof the outer σ of a setting as explained above, for the reasonsexplained above, the outer σ is to be the ratio of the sine of thatangle to the sine of the greatest marginal angle within which 90% of thetotal intensity of the exit pupil lies. For all other illuminationoptics, the following therefore applies:

outer σ=angle value(90% intensity)/sin(γ).

In general, owing to the imaging errors of the illumination optics,different values which may lie between zero and a few mrad are found forthe telecentricity with different σ settings and for the principal raytelecentricity for a given object field point.

The principal ray telecentricity of an object field point is intended tomean the angle of the principal ray relative to the optical axis or anaxis parallel thereto at the position of the object field point. Theprincipal ray is in this case that ray which comes from the geometricalcentre of the exit pupil as seen from the object field point.

Likewise, different values are generally obtained for the telecentricityvalues with annular settings and for the principal ray telecentricityfor a given object field point. An annular setting involves an intensitydistribution in the exit pupil which has not only an outer σ fordelimitation of the light in the exit pupil, but also an inner α. Theinner σ of a setting describes the extent of central shadowing orobscuration in the exit pupil. In the specialist's literature, the innerσ of a setting is intended to mean the ratio of the sine of that angleto the sine of the greatest marginal angle, at which the centralshadowing or obscuration in the exit pupil ends abruptly. For the samereasons as explained above in respect of the outer a, this definition ofthe inner σ of a setting is very suitable for illumination optics inwhich the settings are produced by stops in the pupil planes. For theinner σ of a setting for all other illumination optics, contrary to thisdefinition, in the scope of this application, the inner σ of a settingis to be taken as the ratio of the sine of that angle to the sine of thegreatest marginal angle within which 10% of the total intensity of theexit pupil lies. For all other illumination optics, the followingtherefore applies:

inner σ=angle value(10% intensity)/sin(γ).

The energetic telecentricity on the other hand results from differentparts of the exit pupil having different intensity values, or fromdifferent parts of the exit pupil being differently distorted by theimaging errors of the illumination optics, or better expressed beingdistortedly imaged.

Since the telecentricity is not a unique quantity owing to the differentways of considering it, in the scope of this application the centroidangle value will be used as a unique comparative quantity, i.e. the sineof the centroid angle or of the central ray angle. This quantityincludes both energetic and geometrical causes of the central ray angleof the intensity distribution in the exit pupils, and in the end alsorepresents that quantity which describes the effect of the centroidangle or the central ray angle overall on the imaging process of themask imaging.

A further measure of a deviation of a desired intensity distributionfrom an intensity distribution of an exit pupil of an object fieldpoint, produced in a projection exposure apparatus, is the difference inellipticity between the desired intensity distribution and the achievedintensity distribution.

In order to calculate the ellipticity of an intensity distribution of anexit pupil, the latter is subdivided into four quadrants. Here, thereare two conventional options for arranging the quadrants with respect tothe coordinate system in the object field plane with an x direction anda y direction. In the first arrangement of the quadrants, the exit pupilis divided by one line in the x direction and one line in the ydirection. This division is referred to as xy division.

In the second arrangement, the lines extend at 45° to the xy coordinatesystem. The latter division of the exit pupil is named HV division,since the quadrants lie in horizontal (H) and vertical (V) directionswith respect to the object field.

An ellipticity of an intensity distribution in an exit pupil is nowintended to mean the magnitude value, multiplied by one hundred percent,of the difference between the sum of the intensities in the two Hquadrants of the exit pupil and the sum of the intensities in the two Vquadrants of the exit pupil, normalised to the sum of the two sums. Theellipticity for an XY division of the exit pupil is defined similarly.

A further measure of a deviation of a desired intensity distributionfrom an intensity distribution of an exit pupil of an object fieldpoint, produced in a projection exposure apparatus, is the difference inthe pole balance between the desired intensity distribution and theachieved intensity distribution. In order to calculate the pole balanceof an intensity distribution of an exit pupil, according to the numberof poles or regions with intensity in the exit pupil, the latter iscorrespondingly subdivided into equally large sections radiallysymmetrically about the optical axis. This means that for a dipolesetting having two regions with intensity lying opposite one another inthe exit pupil, the exit pupil is divided into two halves as sections.For a quadrupole setting having four regions with intensity in the exitpupil, the exit pupil is divided into four quadrants as sections.Similarly for n-pole settings having n regions with intensity in theexit pupil, the exit pupil is divided into n sections. A pole balance ofan intensity distribution in an exit pupil is now intended to mean thevalue, multiplied by one hundred percent, of the difference between themaximum intensity of a section of the exit pupil and the minimumintensity of a section of the exit pupil, normalised to the sum of theintensities from the two sections.

Temporal and/or spatial fluctuations of a light source in the scope ofthis application are intended to mean inter alia temporal and/or spatialchanges in the following properties of an illumination ray bundle outputby the light source: position of the illumination ray bundleperpendicularly to the optical axis between the light source and theillumination optics, position of parts of the illumination ray bundlerelative to the rest of the illumination ray bundle perpendicularly tothe optical axis between the light source and the illumination optics,direction of the illumination ray bundle, direction of parts of theillumination ray bundle relative to the direction of the rest of theillumination ray bundle, intensity and polarisation of the illuminationray bundle, intensity and polarisation of parts of the illumination raybundle relative to the intensity and polarisation of the rest of theillumination ray bundle, and any combination of the properties.

Light sources with wavelengths of between 365 nm and 3 nm may beenvisaged as light sources for a projection exposure apparatus formicrolithography, such as high-pressure mercury vapour lamps, lasers,for example excimer lasers, for example ArF₂, KrF₂ lasers or EUV lightsources. In the case of excimer lasers as the light source with atypical wavelengths of 248 nm, 193 nm, 157 nm and 126 nm in the scope ofthis application, inter alia changes in the mode number and modecomposition of the laser modes of the laser pulses of the light sourceare also to be understood as temporal and/or spatial fluctuations of thelight source.

Temporally stabilised illumination of the multi-mirror array (MMA) inthe scope of this application is intended to mean a spatial intensitydistribution of the illumination ray bundle in the plane of themulti-mirror array (MMA), or on the multi-mirror array (MMA), whichchanges with time as a moving ensemble average (see below) or as amoving time average (see below) in its spatial distribution only by lessthan 25 percent, such as less than 10 percent, expressed in terms of theaverage or averaged spatial distribution of all ensemble averages ortime averages. The moving ensemble average is in this case a movingaverage value over an ensemble of light pulses of a pulsating lightsource (see below). The moving time average is correspondingly a movingaverage value over a particular exposure time of a continuous lightsource (see below).

The integral intensity of the intensity distribution, or illumination,over the multi-mirror array (MMA) may in this case very well change verygreatly as a function of time, for example from light pulse to lightpulse, but not the spatial distribution of the illumination over themulti-mirror array (MMA) as a moving ensemble average or as a movingtime average. Furthermore, the average or averaged integral intensity ofthe intensity distribution over the multi-mirror array (MMA) as a movingensemble average or as a moving time average also desirably does notchange greatly, since the dose of an image field point of the projectionexposure apparatus would thereby change greatly, which as a rule isundesirable for the exposure.

A moving ensemble average is intended to mean the moving average valueof a quantity over an ensemble of a number n of successively occurringlight pulses. Here, moving means that the first light pulse of theensemble of n successively occurring light pulses is an arbitrary lightpulse of the light source, and therefore that the ensemble average movesin time with the first light pulse of the ensemble. The situation issimilar with the moving time average over a particular exposure time ofa continuous light source, where the moving average value of a quantityover a particular exposure time moves in time with the starting instantof the exposure time to be considered.

The number n of light pulses of the ensemble, or the particular exposuretime, is determined according to how many light pulses or what exposuretime is or are involved for the exposure of an image field point of theworkpiece to be exposed. Depending on the projection exposure apparatus,ranging from projection exposure apparatus for so-called masklesslithography, through so-called scanners to so-called steppers, theensemble may therefore amount to between one light pulse and severalhundred light pulses, or corresponding exposure times.

Both the structuring of an exit pupil or the intensity distribution inan exit pupil, and the centroid angle value, the ellipticity, the polebalance, the outer and inner σ of an exit pupil of an object field pointof a projection exposure apparatus are to be understood in the scope ofthis application inter alia as further moving ensemble average values ormoving time average values. This is because only these moving ensembleaverage values or moving time average values of a quantity are relevantoverall for the exposure of an image field point, since only thisoverall characterises or describes the illumination or imagingconditions prevailing during the exposure process with the light pulsesof the ensemble or the exposure time.

In some embodiments, the disclosure provides a projection exposureapparatus

-   -   having illumination optics for illuminating an object field with        object field points in an object plane,    -   having projection optics for imaging the object field into an        image field in the image plane,    -   the illumination optics having, for each object field point of        the object field, an associated exit pupil with a greatest        marginal angle value sin(γ) of the exit pupil,    -   the illumination optics containing at least one multi-mirror        array (MMA) having a multiplicity of mirrors for adjusting an        intensity distribution in the associated exit pupils of the        object field points,    -   the illumination optics containing at least one optical system        for temporally stabilising the illumination of the multi-mirror        array (MMA)    -   so that, for each object field point, a first adjusted intensity        distribution in the associated exit pupil deviates from a second        adjusted intensity distribution in the associated exit pupil by        less than the value 0.1 in the outer and/or inner α.

According to the disclosure, a rapid change between annular settingswhich differ only slightly in the outer and/or inner α, via a projectionexposure apparatus having a multi-mirror array (MMA), can be producedparticularly well when temporal stabilisation of the annular settingsrelative to the temporal and/or spatial fluctuations of the light sourceis provided in the form of temporal stabilisation of the illumination ofthe multi-mirror array (MMA).

According to the disclosure, it has been discovered that temporalstabilisation of the illumination of a multi-mirror array (MMA) of aprojection exposure apparatus having fewer than 80,000 mirrors isadvantageous for replicating the light mixing properties of a DOE, asalready described above. It is therefore possible for a change, intendedby the user of the projection exposure apparatus, between two annularsettings differing only slightly in the outer and/or inner σ for theexposure process to be carried out reproducibly with high accuracy,without large fluctuations and with the least possible deviationsrelative to the desired structuring in the form of the annular settings.The user of the projection exposure apparatus according to thedisclosure can therefore change rapidly as well as accurately,temporally stably and reproducibly between two annular settings ordesired intensity distributions in the exit pupils, which differ onlyslightly in the outer and/or inner α.

In certain embodiments, the disclosure refines illumination optics for aprojection exposure apparatus for microlithography having a multi-mirrorarray (MMA) so that, for example, an intensity distribution in the exitpupils of object field points of an object field of the illuminationoptics is stabilised relative to temporal and/or spatial fluctuations ofa light source of the projection exposure apparatus.

This can be achieved, for example, with an illumination optics for aprojection exposure apparatus for microlithography for the homogeneousillumination of an object field with object field points in an objectplane. The illumination optics have an associated exit pupil for eachobject field point of the object field, and the illumination opticscontain at least one multi-mirror array (MMA) having a multiplicity ofmirrors for adjusting an intensity distribution in the associated exitpupils of the object field points. There is an illumination ray bundleof illumination rays between a light source and the multi-mirror array(MMA). The illumination optics contain at least one optical system fortemporally stabilising illumination of the multi-mirror array (MMA). Thetemporal stabilisation is carried out by superposition of illuminationrays of the illumination ray bundle on the multi-mirror array (MMA).

According to the disclosure, superposition of illumination rays of anillumination ray bundle of a light source for the illumination of amulti-mirror array (MMA) advantageously leads to temporal stabilisationof the illumination and therefore to stabilisation of the intensitydistribution in the exit pupils relative to temporal and/or spatialfluctuations of a light source of the projection exposure apparatus.

In some embodiments, the disclosure refines a multi-mirror array (MMA)for illumination optics for a projection exposure apparatus, where themulti-mirror array (MMA) is intended to be suitable for rapidly changingthe structuring of exit pupils of object field points of illuminationoptics of a projection exposure apparatus.

This can be achieved, for example, by a multi-mirror array (MMA), whichis suitable for illumination optics for a projection exposure apparatusfor microlithography having an operating light wavelength λ of theprojection exposure apparatus in the units [nm], where each mirror ofthe multi-mirror array is rotatable about at least one axis through amaximum tilt angle value sin(α) and having a minimum edge length, andthe minimum edge length is greater than 200 [mm*nm]*sin(α)/λ.

The Inventors have discovered that a rapid change between two annularsettings which differ only slightly in the outer and/or inner α, canmore easily be achieved with high accuracy, temporally stably andreproducibly by a projection exposure apparatus having a multi-mirrorarray (MMA), so long as a multi-mirror array (MMA) having more than40,000 mirrors with an edge length of less than 100 μm and a maximumtilt angle of more than 4° is available for this with a wavelength of,for example, 193 nm. This is because the structuring of the exit pupilcan then be composed very finely by spots of the individual mirrors andthe projection exposure apparatus can be accommodated in an installationspace acceptable to the user, as the following considerations will show.

In particular, however, the following considerations also and above allgive handling instructions for multi-mirror arrays (MMA) having fewerthan 40,000 mirrors and/or maximum mirror tilt angles of less than 4°.

The spot of diameter of an individual mirror of the multi-mirror array(MMA) is given, for ideal Fourier optics between the field plane of themulti-mirror array (MMA) and the pupil plane of the Fourier optics, inthis plane by the product of the focal length of the Fourier optics andthe full divergence angle of that part of the illumination ray bundlewhich leaves the individual mirror. On the other hand, the radius of thepupil in the pupil plane is given by the product of the focal length ofthe Fourier optics and the maximum tilt angle of an individual mirror.It follows from this that the ratio of the maximum tilt angle of anindividual mirror to the full divergence angle of the part of theillumination ray bundle after the individual mirror is suitable as ameasure of the resolution or graduation in the pupil plane. A lowdivergence angle and a high maximum tilt angle therefore ensure highresolution in the pupil, as is involved for changing between annularsettings with only a small difference in the outer or inner α. A lowdivergence angle as a first possible way of increasing the resolution inthe pupil, however, also ensures small spots in the pupil and thereforealso little mixing of the light of the spots in the pupil. The effect ofthis is that the structuring of the exit pupil depends on the temporaland/or spatial fluctuations of the light source, cf. the discussionabove of the light mixing properties of a DOE.

A multi-mirror array (MMA) having a large number of mirrors in excess of40,000 can with a very low divergence angle ensure that a region of anexit pupil is illuminated by many mirrors, so as to achieve averagingover these mirrors and therefore decoupling from the temporal and/orspatial fluctuations of the light source. Such a multi-mirror array(MMA) for a projection exposure apparatus for microlithography havingabout 40,000 mirrors can currently be implemented technologically onlywith great difficulty. Furthermore, multi-mirror arrays (MMA) havinghigh values for the maximum tilt angle in excess of 4° are a furtherpossible way of increasing the resolution in the pupil. Suchmulti-mirror arrays (MMA) likewise can currently be implementedtechnologically only with great difficulty.

Besides the resolution in the pupil, the size of the pupil is also aconstraint which may be taken into account.

In a pupil plane of illumination optics, there is generally a fielddefining element (FDE) with intrinsic light mixing or a refractiveoptical element (ROE) with subsequent light mixing in a subsequent fieldplane. The light mixing serves in both cases to generate homogeneousillumination of the object field of the illumination optics. Thefunctional configuration of these elements in the pupil plane involves acertain minimum size of the pupil. The size of the pupil in the pupilplane is determined by the maximum tilt angle and by the focal length ofthe Fourier optics between the multi-mirror array (MMA) and the pupilplane. If the maximum tilt angle cannot be increased further, it istherefore possible for example to increase the focal length of theFourier optics. But since twice the focal length of the Fourier opticsalso defines the distance of the multi-mirror array (MMA) from thesubsequent pupil plane, technical installation space limits areconventionally placed on any arbitrary increase of the focal length.

Besides the resolution in the pupil and the size of the pupil, the lightloss in the illumination optics and the extraneous light in the pupilare also constraints which may be taken into account. The light loss inthe illumination optics leads to a reduction in the throughput ofsubstrates or wafers of a projection exposure apparatus. The extraneouslight in the pupil, for example caused by scattered light or ghostimages, leads in the worst case to certain desired structurings of theexit pupil not being achievable. As a rule, the extraneous light in thepupil will also lead to a change not being possible between annularsettings which differ only slightly in the outer or inner α, since fineresolution in the pupil will be prevented by the extraneous light. Iflight loss and extraneous light are to be avoided in illumination opticshaving a multi-mirror array (MMA), then it is desirable to take intoaccount that there are lower limits for the minimum edge length of amirror of a multi-mirror array (MMA) owing to diffraction effects, andtherefore as a function of the wavelength λ of the illumination light ofthe projection exposure apparatus.

Besides the aforementioned constraints, the costs of illumination opticsmay be taken into account as a further constraint. It follows from thisthat a multi-mirror array (MMA), and therefore the area of theindividual mirror of the multi-mirror array (MMA), also cannot be madearbitrarily large since the area of the multi-mirror array (MMA)together with the maximum tilt angle determine the geometrical flux,which is responsible for the diameter and therefore for the costs of thesubsequent optics. Furthermore, the size of the object field of theillumination optics is thereby likewise co-determined for a givennumerical aperture NA.

The present disclosure utilises the above discoveries in themulti-mirror array (MMA) according to the disclosure for illuminationoptics having a operating light wavelength λ in the units [nm]. Eachmirror of the multi-mirror array (MMA) is in this case rotatable aboutat least one axis through a maximum tilt angle value sin(α) and has aminimum edge length, the minimum edge length being greater than 200[mm*nm]*sin(α)/λ. An advantage thereby obtained with illumination opticshaving such a multi-mirror array (MMA) according to the disclosure isthat it allows a rapid change of the structuring of exit pupils ofobject field points of illumination optics of a projection exposureapparatus, which differ only slightly in the outer and/or inner α. Thischange takes place accurately, temporally stably and reproducibly.

In certain embodiments, the disclosure refines an optical system forhomogenising illumination of a multi-mirror array (MMA) of illuminationoptics for a projection exposure apparatus for microlithography.

This can be achieved, for example, by an optical system for homogenisingillumination of a multi-mirror array (MMA) of illumination optics for aprojection exposure apparatus for microlithography, where the opticalsystem has an illumination ray bundle with a divergence and anillumination light direction from the light source to the multi-mirrorarray (MMA), and the divergence of the illumination ray bundle in theillumination light direction after the optical system is less than fivetimes the divergence of the illumination ray bundle before the opticalsystem.

The Inventors of the present disclosure have discovered that spatialhomogenisation of the illumination of a multi-mirror array (MMA) ofillumination optics by an optical system according to the disclosure ofthe illumination optics ensures temporal stabilisation of theillumination on the multi-mirror array (MMA) and therefore temporalstabilisation of the intensity distribution in the exit pupils. Theillumination of the multi-mirror array (MMA) and the intensitydistribution in the exit pupils are therefore decoupled by thehomogenising optical system from the temporal and/or spatialfluctuations of the light source of the projection exposure apparatus.As mentioned above in the discussion of the relationship of the fulldivergence angle and the resolution in the pupil, the Inventors havefurthermore discovered that the optical system for homogenising theillumination on the multi-mirror array (MMA) desirably does notsubstantially increase the divergence of the illumination ray bundle,since otherwise the desired resolution is not obtained in the pupil fora change of annular settings, which differ only to a small extent in theouter and/or inner α.

In some embodiments, the disclosure refines an optical conditioning unitfor conditioning an illumination ray bundle of a laser for illuminationoptics for a projection exposure apparatus for microlithography.

This can be achieved, for example, by an optical conditioning unit forconditioning an illumination ray bundle of a laser for illuminationoptics for a projection exposure apparatus for microlithography. Thelaser in this case has more than one coherent laser mode and a laseroutput. Furthermore, the illumination ray bundle has a divergence, a rayor bundle profile and a polarisation state. The optical conditioningunit modifies at least the divergence and/or the ray or bundle profileand/or the polarisation state of the illumination ray bundle between thelaser output and the multi-mirror array (MMA).

The Inventors have discovered that under certain circumstances it isfavourable to condition, prepare or modify the size of the illuminationand/or the divergence angle and/or the polarisation state of theillumination ray bundle when it arrives on the multi-mirror array (MMA),so that a rapid change of the structuring of exit pupils of object fieldpoints can be carried out between two annular settings or desiredintensity distributions in the exit pupils, which differ only slightlyin the outer and/or inner α. This is advantageous in particular whenchanging between two annular settings which differ greatly in the sizeof the intensity distribution in the exit pupils. Here, under certaincircumstances, for one of the two settings it is more favourable toselect a different number of mirrors of the multi-mirror array (MMA)and/or a different divergence angle of the illumination ray bundle (seethe above discussion about the effect of the number of mirrors on thestabilisation of an intensity distribution in the exit pupils and aboutthe effect of the full divergence angle of a part of the illuminationray bundle after a mirror on the resolution in the exit pupil).Likewise, for the imaging properties of one of the two settings, it maybe favourable to change the polarisation state. This is alsocommensurately more likely when the two annular settings differ moregreatly in the size of the intensity distribution in the exit pupils.

In certain embodiments, the disclosure provides a method for themicrolithographic production of microstructured components, as well as acomponent which can be produced thereby. The method can include:providing a substrate onto at least some of which a layer of aphotosensitive material is applied; providing a mask, which includesstructures to be imaged; and/or providing an optical conditioning unitfor illumination optics; and/or providing an optical system forillumination optics; and/or providing a multi-mirror array forillumination optics; and/or providing illumination optics for aprojection exposure apparatus; and/or providing a projection exposureapparatus; projecting at least a part of the mask onto a region of thelayer with the aid of projection optics of the projection exposureapparatus to produce a microstructured component.

In some embodiments the optical system, which is configured to produce atemporal modification of the incoherent superposition, includes amirror, which has a mirror surface, and an actuator which is configuredto produce a tilt of at least a portion of the mirror surface. Bytilting at least a portion of the mirror surface illumination raybundles are tilted as well and obliquely impinge on the opticalintegrator. This results in a lateral shift of the intensitydistribution produced on the subsequent multi-mirror array. If theoptical integrator includes two channel plates of a honeycomb condenser,it is possible to change the surface area on the channels of the secondplate illuminated by illumination ray sub-bundles. This may preventdamages in the second channel plate which otherwise may be caused by toohigh intensities which occur if the first channel plate focuses theillumination ray sub-bundles on the second channel plate.

The concept of directing ray bundles onto channels (i.e. microlenses) ofan optical integrator with temporarily varying angles of incidence mayalso be used if the superposition of incoherent illumination ray bundlesis of no concern. Also in this case this concept avoids damages in ahoneycomb optical integrator including two plates each including aplurality of microlenses.

A tilt of at least a portion of the mirror surface may be produced withthe help of actuators that bend the mirror surface. In some embodiments,the actuator is configured to produce rotary oscillations of the mirroraround a rotary axis, which is inclined to the optical axis by an angledistinct from 0°, such as by an angle of 90°. By controlling theamplitude of the rotary oscillations, it is possible to adapt the tiltof the mirror surface, which is produced by the rotary oscillations, tothe specific desired properties which may change during the operation ofthe apparatus. For example, the divergence of the illumination raysub-bundles has a strong effect on the size of the illuminated area onthe channels of the second channel plate. If this divergence varies as aresult of various influences, for example changing optical properties ofoptical elements as a result of heating effects, the amplitudes of therotary oscillations may be adapted to the changing desired properties.

If the mirror shall be optically conjugated to the micro-mirror array,an arrangement may be desirable in which the mirror and the micro-mirrorarray are arranged in parallel planes. In this respect it may beadvantageous if the optical system includes a polarization dependentbeam splitting surface and a polarization manipulator which is arrangedbetween the beam splitting surface and the mirror. Then it is possibleto use the polarization dependent beam splitting surface as a foldingmirror which is transparent for light which has been reflected from themirror and has passed twice through the polarization manipulator.

In some embodiments, the illumination ray bundle has a divergence and anillumination light direction from the light source to the multi-mirrorarray. The divergence of the illumination ray bundle in the illuminationlight direction after the optical system is less than twice thedivergence of the illumination ray bundle before the optical system.

In some embodiments, the object field has an illuminated object fieldsurface has a size OF, and an illuminated surface of the multi-mirrorarray has a size AF, where AF=c*sin(γ′)/sin(α)*OF, c is a constant with0.1<c<1, and sin(γ′) is the greatest marginal angle value among thegreatest marginal angle values sin(γ) associated with the exit pupils ofthe object field points. An average reflectivity of the mirrors of themulti-mirror array for an angle of incidence between 0° and 60° is morethan 25%. A standard deviation of the reflectivity of the mirrors of themulti-mirror array from the average reflectivity is, for an angle ofincidence between 0° and 60°, less than 50% expressed in terms of theaverage reflectivity. The apparatus is configured for being operated asa scanner, and the intensity distribution of the exit pupils of theobject field points are modified during the scan process. An illuminatedsolid angle range in the exit pupil associated with an object fieldpoint, which range is generated by a mirror of the multi-mirror array,has a maximum angle range value which is less than 5% expressed in termsof the greatest marginal angle value sin(γ) of the associated exitpupil. A solid angle range in the exit pupil associated with an objectfield point is illuminated with a non-zero intensity and an angle rangevalue of less than 10% expressed in terms of the greatest marginal anglevalue of the associated exit pupil by at least two mirrors of themulti-mirror array. The greatest marginal angle value sin(γ) of the exitpupil associated with an object field point is greater than 0.2 for allobject field points. At least one mirror of the multi-mirror array has adifferent surface content than another mirror of the multi-mirror array.At least one mirror of the multi-mirror array has a different shortestdistance from its closest neighbouring mirror than another mirror of themulti-mirror array. The illumination optics includes at least twomulti-mirror arrays, the at least two multi-mirror arrays differing fromeach other in at least one property of a mirror. The illumination opticsfurther contain at least one optical system to temporally stabilize theillumination of the multi-mirror array so that, for each object fieldpoint, the intensity distribution in the associated exit pupil deviatesfrom a desired intensity distribution in the associated exit pupil inthe case of a centroid angle value sin(β) by less than 2% expressed interms of the greatest marginal angle value sin(γ) of the associated exitpupil and/or, in the case of ellipticity by less than 2%, and/or in thecase of a pole balance by less than 2%. The optical system can includean optical integrator. The integrator can be honeycomb condenser havinga focal length of more than 5 m.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features and advantages of the present disclosure may be morereadily understood with reference to the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 schematically shows a projection exposure apparatus formicrolithography having illumination optics with a rod as an integratoras prior art;

FIG. 2 schematically shows a projection exposure apparatus formicrolithography having illumination optics with an FDE as an integratoras prior art;

FIG. 3 schematically shows a pupil forming unit according to thedisclosure of illumination optics according to the disclosure having amulti-mirror array (MMA) according to the disclosure;

FIG. 4 schematically shows an optical system according to the disclosurefor stabilising the illumination of a multi-mirror array (MMA) accordingto the disclosure;

FIG. 5 schematically shows an optical system according to the disclosurefor stabilising the illumination of a multi-mirror array (MMA) accordingto the disclosure with an intensity distribution over the multi-mirrorarray according to the disclosure;

FIG. 6 schematically shows an optical system according to the disclosurefor stabilising the illumination of a multi-mirror array (MMA) accordingto the disclosure with a periodic phase element according to thedisclosure;

FIG. 7 schematically shows an optical system according to the disclosurefor stabilising the illumination of a multi-mirror array (MMA) accordingto the disclosure with a phase element according to the disclosurehaving a random phase profile;

FIG. 8 schematically shows an optical system according to the disclosurefor stabilising the illumination of a multi-mirror array (MMA) accordingto the disclosure with a rotating phase element according to thedisclosure;

FIG. 9 schematically shows a beam path of an illumination ray bundle asfar as the first pupil plane after the pupil forming unit according tothe disclosure;

FIG. 10 schematically shows a beam path of an illumination ray bundle asfar as the first pupil plane after the pupil forming unit according tothe disclosure with a lens array according to the disclosure;

FIG. 11 schematically shows a conditioning unit according to thedisclosure for conditioning the illumination of a multi-mirror array(MMA) according to the disclosure with a mixing and/or scatteringelement according to the disclosure;

FIG. 12 schematically shows a conditioning unit according to thedisclosure for conditioning the illumination of a multi-mirror array(MMA) according to the disclosure with a mixing and/or scatteringelement according to the disclosure and a symmetrising unit according tothe disclosure;

FIG. 13 schematically shows a symmetrising unit according to thedisclosure for a conditioning unit according to the disclosure;

FIG. 14 schematically shows a conditioning unit according to thedisclosure for conditioning the illumination of a multi-mirror array(MMA) according to the disclosure with a mixing and/or scatteringelement according to the disclosure and a symmetrising unit according tothe disclosure and a stop according to the disclosure;

FIG. 15 schematically shows a phase element according to the disclosurefor a conditioning unit according to the disclosure;

FIG. 16 schematically shows an optical system according to thedisclosure for stabilising the illumination of a multi-mirror array(MMA) according to the disclosure with a honeycomb condenser accordingto the disclosure as an integrator according to the disclosure and tele-or relay optics according to the disclosure;

FIG. 17 schematically shows an optical system according to thedisclosure for stabilising the illumination of a multi-mirror array(MMA) according to the disclosure with a rod according to the disclosureor a light guide according to the disclosure as an integrator accordingto the disclosure and tele- or relay optics according to the disclosure;

FIG. 18 schematically shows an optical system according to thedisclosure for stabilising the illumination of a multi-mirror array(MMA) according to the disclosure with a plate mixer condenser accordingto the disclosure as an integrator according to the disclosure and tele-or relay optics according to the disclosure;

FIG. 19 schematically shows an optical system according to thedisclosure for stabilising the illumination of a multi-mirror array(MMA) according to the disclosure with a cube mixer according to thedisclosure as an optical conditioning unit according to the disclosure,which simultaneously serves as a simple integrator according to thedisclosure, and tele- or relay optics according to the disclosure;

FIG. 20 schematically shows a meridional section through an opticalsystem of the disclosure for stabilizing the illumination of amulti-mirror array, including a mirror which is capable of performingrotary oscillations;

FIGS. 21 to 23 schematically show the illumination of a honeycombcondenser including two channel plates at three different instants, atwhich illumination ray sub-bundles impinge under different angles ofincidence on the first channel plate;

FIG. 24 schematically shows a cross-section through a mixing elementaccording to an embodiment in which evanescent waves propagate betweentwo rods spaced apart by a small distance;

FIG. 25 schematically shows a mixing unit including a plurality ofmixing elements as shown in FIG. 24;

FIG. 26 schematically shows a mixing element according to anotherembodiment in which two rods are spaced apart by a thin layer of wateror another dielectric medium;

FIG. 27 schematically shows a mixing element according to a stillfurther embodiment including a slab similar to a Lummer-Gehrke plate.

DETAILED DESCRIPTION

FIG. 1 schematically shows an example of a prior art projection exposureapparatus for microlithography. A light source 1 generates anillumination ray bundle 12 whose cross section is changed in beamexpansion optics 14. The illumination ray bundle 12 then impinges on adiffractive optical element 3 a (DOE). The diffractive optical element 3a is arranged in a field plane of the illumination optics and generatesan illumination angle distribution according to diffractive structuresthat are contained in the diffractive optical element 3 a. Then, withthe illumination angle distribution imposed by the diffractive opticalelement, the illumination ray bundle 12 passes through the opticalmodule 2 and a subsequent pupil plane. This pupil plane (not indicatedin FIG. 1) is arranged in the vicinity of a refractive optical element 3b. For further modifying the illumination ray bundle 12, the opticalmodule 2 includes a zoom system schematically represented by a axiallydisplaceable lens 22 and a pair of axicon elements 21. By retracting theaxicon elements 21 from one another, it is possible to adjust the innerσ of a setting, or the borders of the cross section of the illuminationray bundle of an illumination setting. On the other hand, by changingthe focal length of the zoom system, which involves a displacement of atleast one lens 22 along the optical axis, it is possible to adjust theouter σ of an illumination setting, or generally the outer border of theillumination ray bundle cross section. By suitable configuration of thediffractive optical element 3 a and by suitable selection of theposition of the axicon elements 21 and of the zoom lens 22, it ispossible to generate almost any desired intensity distribution at theoutput of the optical module 2, namely in the pupil plane arranged inthe vicinity of the refractive optical element 3 b.

The refractive optical element 3 b imposes a field angle distribution onthis intensity distribution of the illumination ray bundle 12 in thepupil plane, in order to obtain a desired field shape in a field plane,for example a rectangular field shape with an aspect ratio of 10:1. Thisfield angle distribution of the illumination ray bundle 12 in the pupilplane is transferred by the subsequent field lens optics 4 into anillumination field 5 e at the input of a rod 5. The illuminated field 5e at the input of the rod 5 lies in a field plane of the illuminationoptics and has an illumination angle distribution with a maximumillumination angle value which as a rule, but not necessarily,corresponds to the numerical aperture of the preceding field lens optics4. In contrast to the field at the diffractive element 3 a, the field 5e has the full geometrical flux of the illumination optics. Thisgeometrical flux is the result of a twofold introduction of geometricalfluxes. First, geometrical flux for the pupil is introduced by thediffractive optical element 3 a in order to adjust the illuminationangle distribution in a subsequent field plane. In a second step,geometrical flux for the field is introduced by the refractive opticalelement 3 b in order to adjust the illuminated field shape in thesubsequent field plane, so that the full geometrical flux of theillumination optics is available subsequent to the optical element 3 b.

The illuminated field 5 e at the input of the rod 5 is transferred bythe rod 5 to the output of the rod into a field 5 a. The maximumillumination angles in the field 5 a of the rod output correspond tothose in the field 5 e of the rod input. Multiple total reflections atthe rod walls of the rod 5 create, at the rod exit in the exit pupils ofthe field points of the field 5 a, secondary light sources with thefield shape of the field 5 e at the rod entry as the shape of eachindividual secondary light source. By this kaleidoscope effect of therod 5, the field 5 a is homogenised in respect of the intensitydistribution over the field since the light of many secondary lightsources is superposed in this field 5 a.

A field stop 51 delimits the field 5 a in its lateral extent and ensuresa sharp bright-dark transition of the field. A subsequent, so-calledREMA objective 6 images the field 5 a into the reticle plane 7. Thebright-dark edges of the field stop 51 are thereby transferred sharplyinto the object or field plane 7. This function of the sharp edgeimaging of the field stop 51 into the reticle or field plane 7, alsoreferred to as “reticle masking”, leads to the name REMA(REticleMAsking) of this objective. The REMA objective 6 consists forexample of a condenser group 61, a pupil region in the vicinity of apupil plane 62, a pupil lens group 63, a deviating mirror 64 and asubsequent field lens group 65.

In the pupil region 62 of the REMA objective, for example, a widevariety of manipulations of the pupil may be carried out, particularlywith regard to transmission or polarisation. The REMA objective 6ensures imaging of the field 5 a with the sharp field edges of the fieldstop 51 into the reticle plane (i.e. field plane 7). The illuminationangle distribution of the field 5 a is thereby also transferred into acorresponding illumination angle distribution in the field plane 7. Eachobject field point of the illumination field in the reticle plane (i.e.field plane 7) therefore obtains its illumination angle distribution, orits exit pupil.

In general, a REMA objective 6 illuminates the reticle or field plane 7telecentrically, i.e. the illumination angle distribution of everyobject field point is symmetrical about the optical axis or an axisparallel thereto. The backward geometrical extension of the illuminationlight rays at an object field point of the field plane 7, in thedirection of the illumination optics or light source 1, gives atinfinity the virtual exit pupil of the illumination optics for thisobject field point. The forward projection of the illumination angledistribution of an object field point in the object field plane 7, inthe direction of the subsequent projection optics 8, gives at infinity areal exit pupil of the illumination optics for this object field pointbeing considered. The virtual or real exit pupil of the illuminationoptics is a direct consequence in the case of a telecentric beam path ofthe illumination optics in the field plane 7. The height of a point inthe exit pupil relative to the centre of the exit pupil of an objectfield point is in this case given by the tangent of the illumination rayangle of this object field point multiplied by the distance of the exitpupil.

The object field plane 7 represents the dividing plane betweenillumination optics and projection optics, for example a projectionobjective 8, of a projection exposure apparatus. The illumination opticshave the task of homogeneously illuminating a field delimited with sharpedges, and thereby producing a desired illumination angle distributionor exit pupil of an object field point according to the specifications.

In the scope of this application, the production of an illuminationangle distribution of an object field point is equivalent in meaninghere to producing an intensity distribution in the exit pupil of thisobject field point, since a particular illumination angle of an objectfield point is related via the tangent conditions to the correspondingposition in the exit pupil.

Reticles or masks for chip production are introduced into the objectfield plane 7. These masks are illuminated via the illumination raybundle 12 produced by the illumination optics. The projection objective8 images the illuminated mask into a further field plane, the imagefield plane 10. There a substrate 9 is arranged which supports aphotosensitive layer on its upper side. The mask structures aretransferred by the projection objective 8 into corresponding exposedregions of the photosensitive layer. Generally speaking, there are twodifferent types of projection exposure apparatus in this case, theso-called stepper in which the entire mask field is transferred onto thephotosensitive substrate 9 in one exposure step, and the so-calledscanner in which only parts of the mask are transferred onto parts ofthe substrate 9 in an exposure step, the mask and the substrate in thiscase correspondingly being moved in a synchronised fashion in order totransfer the entire mask.

After the exposure process step, the exposed substrate 9 is subjected tosubsequent process steps, for example etching. As a rule, the substrate9 subsequently receives a new photosensitive layer and is subjected to anew exposure process step. These process steps are repeated until thefinished microchip, or the finished microstructured component, isobtained.

FIG. 2 schematically shows another example of a prior art projectionexposure apparatus for microlithography. The elements in FIG. 2 whichcorrespond to those in FIG. 1 are denoted by the same referencenumerals.

The projection exposure apparatus in FIG. 2 differs from the projectionexposure apparatus in FIG. 1 merely in the illumination optics. Theillumination optics in FIG. 2 differ from the illumination optics inFIG. 1 in that the rod 5 for generating secondary light sources isabsent. Furthermore, the illumination optics in FIG. 2 differ in that afield defining element 3 c (FDE) ensures not only generation of theinvolved field angles in the pupil plane but also, through constructionas a two-stage honeycomb condenser, generation of the secondary lightsources. The field defining element 3 c in FIG. 2 therefore includesboth the functionality of the refractive optical element (ROE) 3 b inFIG. 1 and the functionality of the rod 5 in FIG. 1. The field definingelement 3 c, configured as a two-stage honeycomb condenser, on the onehand introduces the field angle in the pupil plane and on the other handgenerates the secondary light sources in the pupil plane. Acorresponding field shape, with a desired homogenised intensitydistribution over the field, is therefore generated in the subsequentfield planes of the illumination optics by the superposition of light ofthe secondary light sources.

FIG. 3 schematically shows a pupil forming unit according to thedisclosure for illumination optics for a lithographic projectionexposure apparatus, as is represented for example in FIG. 1 or 2. Here,the pupil forming unit according to the disclosure in FIG. 3 serves as areplacement for the pupil forming unit 2 of this projection exposureapparatus according to FIG. 1 or 2. Use of the pupil forming unit ofFIG. 3 is however not limited to these projection exposure apparatus asrepresented in FIG. 1 or 2.

The pupil forming unit of FIG. 3 ends in the pupil plane 44, which isarranged, in the exemplary embodiment shown in FIG. 1, in the vicinityof the refractive optical element 3 b, and, in the exemplary embodimentshown in FIG. 2, in the vicinity of the field defining element 3 c.Instead of the diffractive optical element 3 a of FIGS. 1 and 2, amulti-mirror array (MMA) 38 produces an illumination angle distributionwhich is superposed in the pupil plane 44 to form an intensitydistribution in this pupil plane. This intensity distribution of thepupil planes 44 corresponds to the intensity distribution in the exitpupil 143, or the illumination angle distribution of an object fieldpoint, so long as ideal Fourier optics are assumed.

An illumination ray bundle 12 coming from a light source and deviated bya plane folding mirror 30 is decomposed by a honeycomb condenser 32 intoindividual illumination ray sub-bundles and subsequently guided by relayoptics 34, or a condenser 34, onto a lens array 36. This lens array 36concentrates the illumination ray sub-bundles onto the individualmirrors of the multi-mirror array 38. The individual mirrors of themulti-mirror array 38 can be tilted differently, i.e. at least some ofthe mirrors of the multi-mirror array are rotatable about at least oneaxis in order to modify an angle of incidence of the associatedillumination ray sub-bundle, so that different intensity distributionscan be adjusted in the pupil plane 44. The illumination ray sub-bundlescoming from the mirrors of the multi-mirror array 38 pass through asubsequent scattering disc 40 and condenser optics 42 so that theyintersect, now desirably with parallel principal rays, the pupil plane44.

FIG. 4 shows the section of FIG. 3 between the plane folding mirror 30and the multi-mirror array 38 schematically and on an enlarged scale. Inthis illustration the optional lens array 36 between the condenseroptics 34 and the multi-mirror array 38 is not shown. FIG. 4 shows anillumination ray sub-bundle of the illumination ray bundle 12 as itpasses through the honeycomb condenser 32 and the condenser 34 onto themulti-mirror array 38. In this exemplary embodiment the condenser 34forms Fourier optics having a front focal plane, in which a secondhoneycomb channel plate of the honeycomb condenser 32 is arranged, and arear focal plane, in which the multi-mirror array 38 is arranged. Theray paths of selected rays of the illumination ray sub-bundle arerepresented in the form of solid and dashed lines, and the optical axisis represented in the form of a dot-and-dash line. The ray pathsrepresented as solid line indicate rays which strike a first honeycombchannel plate of the honeycomb condenser 32 at an angle which is aslarge as possible. The ray paths represented in dashed form indicaterays which strike the first honeycomb channel plate of the honeycombcondenser 32 parallel to the optical axis, and therefore at an anglewhich is as small as possible.

The divergence of the illumination ray sub-bundle in front of thehoneycomb condenser 32 is therefore given by the full aperture anglebetween the ray paths of the illumination rays of the illumination raysub-bundle in the form of the solid line. This divergence is representedsymbolically in FIG. 4 by the filled circle a. The filled area of thecircle a is intended to be a measure of the divergence of theillumination ray sub-bundle.

After the honeycomb condenser 32, it is the ray paths represented asdashed lines which determine the divergence of the illumination raysub-bundle. This divergence is in turn represented symbolically in theform of a filled circle b. The filled circle b has a larger area thanthe filled circle a before the honeycomb condenser, and thereforerepresents the divergence-increasing effect of a honeycomb condenser 32on an illumination ray sub-bundle.

FIG. 5 shows how two illumination ray sub-bundles (indicated with solidand dashed lines) of the illumination ray bundle 12 pass through twohoneycomb channels of the honeycomb condenser 32 and impinge on themulti-mirror array 38. Both ray paths of the two illumination raysub-bundles are associated with rays which arrive parallel to theoptical axis and therefore perpendicularly on the honeycomb condenser32. With the aid of FIG. 5, it may be seen that the two ray paths of thetwo illumination ray sub-bundles are superposed on the multi-mirrorarray 38 by the condenser 34. This is also illustrated with the aid ofthe ray paths 12 a and 12 b from the two honeycomb channels of thehoneycomb condenser 32. The ray paths 12 a and 12 b are superposed atthe same position on the multi-mirror array 38, even though they comefrom two different honeycomb channels.

If the two illumination ray sub-bundles shown in FIG. 5 have a highmutual spatial coherence, this can lead to periodic intensity variationson the multi-mirror array 38 when the two illumination ray sub-bundlesare superposed on the multi-mirror array 38. Exemplary variations ofthis kind are illustrated in FIG. 5 by a function 100. This function 100changes periodically between a maximum and minimum value as a functionof the position over the multi-mirror array 38.

FIG. 6 schematically shows an exemplary embodiment which differs fromthe exemplary embodiment shown in FIG. 5 in that it includes a periodicphase element 33 a which is used to avoid the spatial coherence. Theupper part of FIG. 6 shows ray paths of the two illumination raysub-bundles passing through the upper two honeycomb channels of thehoneycomb condenser 32 similar to what has been shown in FIG. 5. It isassumed that the two illumination ray sub-bundles, which originate froman illumination ray sub-bundle 121 associated with the two upperhoneycomb channels of the honeycomb condenser 32, are mutually spatiallycoherent.

However, as a result of the periodic phase element 33 a arranged betweenthe two honeycomb channel plates of the honeycomb condenser 32, the twoillumination ray sub-bundles of the upper two honeycomb channels of thehoneycomb condenser 32 are mutually shifted in phase, so that, inaddition to the first spatially periodic intensity distribution over themulti-mirror array 38, a second spatially periodic intensitydistribution over the multi-mirror array 38 is obtained which isspatially shifted relative to the first. The function 100 a shows thesetwo mutually spatially shifted periodic intensity distributions over themulti-mirror array 38. It may be seen clearly that the intensity as asum of these two periodic intensity distributions no longer variesbetween the maximum value and the minimum value, but instead onlybetween the maximum value and an average value. This means that owing toits periodic phase function, the phase element 33 a leads to a reductionin the spatial interference phenomena over the multi-mirror array 38 dueto the spatial coherence of the illumination ray sub-bundles. What hasbeen the applies accordingly for the lower illumination ray sub-bundle122 from which two mutually spatially coherent illumination raysub-bundles originate and pass through the two lower honeycomb channelsof the honeycomb condenser 32.

FIG. 7 schematically shows an alternative exemplary embodiment in whicha phase element 33 b having an arbitrary phase function is arranged infront of the honeycomb condenser 32 for reducing the spatialinterference phenomena in the intensity distribution on the multi-mirrorarray 38. The desired second spatial intensity distribution on themulti-mirror array 38 is in this case produced by the two illuminationray sub-bundles passing through the lower two honeycomb channels of thehoneycomb condenser 32. These two illumination ray sub-bundles aretilted by the phase element 33 b before they enter the honeycombcondenser 32. Owing to the tilting before the honeycomb condenser 32,the two mutually spatially coherent illumination ray sub-bundlesoriginating from the incident illumination ray sub-bundle 122 areshifted inside the second honeycomb condenser plate of the honeycombcondenser 32 so as to obtain a spatially shifted second periodicintensity distribution over the multi-mirror array.

The function 100 b represents the two mutually spatially shiftedperiodic intensity distributions on the multi-mirror array 38. It may beseen that the total intensity as a sum of the two periodic intensitydistributions now no longer varies between a maximum value and a minimumvalue, but instead the intensity varies merely between a maximum valueand an averaged value. In contrast to the exemplary embodiment shown inFIG. 6, the variations of the spatial intensity distribution on themulti-mirror array 38, which are due to the spatial coherence of theillumination ray sub-bundles, are reduced not by two spatially coherentillumination ray sub-bundles contributing to two separate, mutuallyspatially shifted intensity distributions owing to a periodic phaseelement. Instead, this reduction is achieved by the two illumination raysub-bundles with their spatial coherence contributing to a periodicintensity distribution which is shifted by the phase element 33 brelative to the periodic intensity distribution of other spatiallycoherent illumination ray sub-bundles.

FIG. 8 schematically shows another exemplary embodiment in which a phaseelement 33 c reduces the effect of the spatial coherence of illuminationray sub-bundles on the intensity distribution produced on themulti-mirror array 38. The phase element 33 c is, in this exemplaryembodiment, configured as a rotatable wedge. This wedge ensures that thespatial intensity distribution on the multi-mirror array 38 migrates toand fro as a function of time so that a time-averaged total intensitydistribution varies between a maximum value and an averaged value. Theintensity distribution 100 c shown in FIG. 8 represents an instantaneouspicture of the spatial intensity distribution over the multi-mirrorarray 38 for an arbitrary fixed position of the rotatable phase element33 c. When the phase element 33 c rotates, this intensity distribution100 c periodically moves over the mirror array 38, as it is indicated bythe double arrow shown in FIG. 8. Thus the intensity distribution on themulti-mirror array 38 is shifted as a function of time over the surfaceof the mirror array 38, which results in the intensity on a mirror ofthe multi-mirror array being averaged out over time.

FIG. 9 schematically shows beam paths of the illumination ray bundle 12.The rays enter the honeycomb condenser 32, are reflected from one of theindividual mirrors 38 s of the multi-mirror array and finally passthrough the pupil plane 44. The ray paths indicated by solid linesdenote those illumination rays which pass through marginal zones (in theoptical sense) of the individual channels of the honeycomb condenser 32.The ray paths indicated by dashed lines denote those illumination rayswhich pass right through the margins of the channels of the honeycombcondenser 32. The dot-and-dash line in FIG. 9 represents the opticalaxis.

All the rays shown in FIG. 9 emerging from the honeycomb condenser 32pass through the condenser 34 and fall onto one of the individualmirrors 38 s of the multi-mirror array 38. After being reflected fromthe mirror 38 s, the rays are superposed on a surface element 44 a ofthe pupil plane 44 with the help a further condenser 42. It is notedthat the mirror 38 s is shown in FIG. 9, for the sake of simplicity, asif it was transparent. In reality the condenser 42 and the pupil plane44 are arranged along on optical axis which is inclined with regard tothe optical axis on which the honeycomb condenser 34 is centred.

The condenser 42, which is arranged after the multi-mirror array in thepropagation direction of the illumination ray bundle 12, is optional andmay be omitted, particularly if curved mirrors 38 s are used.

FIG. 10 shows beam paths similar to what has been shown in FIG. 9. Inthis exemplary embodiment, however, a lens array 36 is arranged betweenthe condenser 34 and the multi-mirror array 38 including individualmirrors 38 s. The lens array 36 ensures stronger concentration(focusing) of the rays on the individual mirrors 38 s of themulti-mirror array 38. In the exemplary embodiment shown in FIG. 10, therays indicated with solid and dashed lines are no longer superposed inthe pupil plane 44 on a pupil element 44 a by the subsequent condenser42, but instead are positioned adjacent to one another so that theyilluminate a larger surface element 44 b in the pupil plane 44. Bysuitably dimensioning of the lens array 36, of a curvature of thereflecting surface of the individual mirrors 38 s and of the condenser42, it is possible to determine the size of the surface element 44 billuminated in the pupil plane by the individual mirror. As a result ofsuch dimensioning, the surface element 44 b illuminated in the pupilplane 44 may also be equal to or smaller than the corresponding surfaceelement 44 a in the exemplary embodiment shown in FIG. 9.

FIG. 11 schematically shows another exemplary embodiment of thedisclosure. Rays if an illumination ray bundle 12 are shown which entera pupil forming unit and impinge on the multi-mirror array 38 of thepupil forming unit. The pupil forming unit of this exemplary embodimentincludes a diffractive optical element 3 d and a condenser or Fourieroptics 34. The multi-mirror array 38 of this exemplary embodimentincludes individual mirrors 38 s as shown in the detail image. Theindividual mirrors 38 s can be tilted about one or more axes. It is thuspossible for the light rays incident on the individual mirrors 38 s tobe reflected in different, adjustable emergence directions.

The diffractive optical element 3 d has the task of decomposing theillumination ray bundle 12 into a large plurality of illumination raysub-bundles and superposing these illumination ray sub-bundles with theaid of the condenser 34 onto the individual mirrors 38 s of themulti-mirror array 38, and at the same time concentrating or focusingthem onto the individual mirrors 38 s. This is represented schematicallyin a further detail view by the regions 381 illuminated on therespective individual mirrors 38 s of the multi-mirror array 38.

FIG. 12 schematically shows an optical conditioning unit 400 which maybe arranged in front of the pupil forming unit shown in FIG. 11. Theoptical conditioning unit 400 receives the illumination ray bundle 12,which has a certain intensity profile 401. At its output the opticalconditioning unit 400 produces an illumination ray bundle which issymmetrical with respect to an optical axis (not shown in FIG. 12),wherein this illumination ray bundle has intensity sub-profiles 402 and403 above and below the optical axis, respectively. At the output of thepupil forming unit including the DOE 3 d, the condenser 34 and themulti-mirror array 38, according to FIG. 11, superposition of the twointensity profiles 402 and 403 takes place.

FIG. 13 schematically shows a detail of an exemplary embodiment of anoptical conditioning unit 400 that is used in the exemplary embodimentshown in FIG. 12 and produces symmetrical intensity profiles 402 and403. The illumination ray bundle 12 with the intensity profile 401 and alinear polarisation, which is perpendicular to the plane of the drawingas indicated in FIG. 13 by small circle symbols, is partiallytransmitted through a semitransparent mirror 505. Behind the mirror 505,i.e. at the output of the optical conditioning unit 400, theillumination ray bundle has an intensity profile 402 and is linearlypolarised with a polarization direction perpendicular to the plane ofthe drawing.

The other part of the illumination ray bundle 12 is reflected at thesemitransparent mirror 505 while preserving the polarisation. Thisreflected part is reflected again by a polarization dependent beamsplitter 504 in a direction counter to the original light direction ofthe illumination ray bundle 12. This part of the illumination ray bundle12 subsequently passes through a λ/4 plate 502, which may also bereplaced by an optical rotator that rotates the polarization directionby 45°. The state of polarisation of this part of the illumination raybundle 12 is thereby converted into a circular polarisation (notrepresented). This converted part of the illumination ray bundle 12 issubsequently reflected at the mirror 501 and again passes through theλ/4 plate 502 on its return path. The circular polarisation of the lightis thereby converted into a linear polarisation with a polarizationdirection parallel to the plane of the drawing.

It is therefore possible for the remaining part of the illumination raybundle 12 to pass through the polarizer 504 on the return path aslinearly polarised light with a polarization direction being parallel tothe plane of the drawing. A subsequent λ/2 plate 503 rotates thepolarisation direction of the linearly polarised light back from theorientation parallel to the plane of the drawing to an orientationperpendicular to the plane of the drawing, so that a second intensityprofile 403 with a linear polarisation perpendicular to the plane of thedrawing is obtained at the output of the optical conditioning unit 400.This intensity profile 403 has a mirror-symmetric intensity shape withrespect to the intensity profile 402.

FIG. 14 shows an exemplary embodiment which differs from the exemplaryembodiment shown in FIG. 12 in that an additional stop device 600 isprovided. The stop device 600 is used to delimit the illumination raybundle 12 having the symmetrized intensity profiles 402 and 403, so thatany scattered light generated in the conditioning unit 400 canadvantageously be stopped out.

FIG. 15 schematically shows a phase element 701 which may optionally bearranged in front of the diffractive optical element 3 d of theexemplary embodiment according to one of FIGS. 11, 12 and 14. The phaseelement 701, which may be or include an aspherical lens element and/or alens element with a freeform surface, serves to adapt the wavefront 700of the illumination ray bundle 12. FIG. 15 shows a wavefront 700 of theillumination ray bundle 12 before it passes through the phase element701. FIG. 15 furthermore shows the wavefront 702 of the illumination raybundle 12 after the phase element 701. It may be seen clearly that thewavefront 702 after passing through the phase element 701 has, forexample, a smaller curvature than the original wavefront 700 of theillumination ray bundle 12. By suitable selection of the phase element701, it is therefore possible to modify the wavefront of theillumination ray bundle 12 before it enters the illumination optics of aprojection exposure apparatus for microlithography. By modifying thecurvature of the wavefront of an illumination ray bundle 12, itsdivergence is also changed. The phase element 701 in FIG. 15 thereforeserves not only to modify the curvature of the wavefront of anillumination ray bundle 12, but also to modify or condition thedivergence of the illumination ray bundle 12.

FIG. 16 schematically shows a pupil forming unit according to thedisclosure including a honeycomb condenser 32, condenser or relay ortele-optics 34, a lens array 36 and a multi-mirror array 38. Since thehoneycomb condenser 32, as shown in FIG. 4, does not substantiallyincrease the divergence of the illumination ray bundle, it is desirableto use a condenser or relay optics 34 having a large focal length inorder to be able to convert these low divergences into correspondingheights relative to the optical axis on the multi-mirror array 38. Fortechnical installation space reasons, it is therefore expedient for thiscondenser or relay optics 34 having a large focal length to be folded byprisms or mirrors.

FIG. 17 schematically shows an alternative pupil forming unit in which,compared with the exemplary embodiment shown in FIG. 16, the honeycombcondenser 32 has been replaced by a suitable rod 32 a, a light-guidingoptical fibre 32 a or a light-guiding fibre bundle 32 a.

FIG. 18 schematically shows another exemplary embodiment of a pupilforming unit according to the disclosure. In this exemplary embodimentthe relay or condenser optics 34 are divided into two separate relayoptics 34 a and 34 b. In contrast to the previous exemplary embodiments,an optical system, which is formed by “auxiliary lenses” of two thinoptical plates placed mutually perpendicularly, is used as the lightmixing instrument 32 b in FIG. 18. The two thin plates placed mutuallyperpendicularly ensure the desired light mixing effect on themulti-mirror array 38.

In the exemplary embodiment shown in FIG. 18, an optional beam formingunit 31 a ensures adaptation of the size and the divergence of theillumination ray bundle. It is indicated by two section planes 31 bperpendicular to the ray propagation direction that elements accordingto the disclosure of the pupil forming unit and/or of the conditioningunit of the illumination optics may also lie before the housing wall ofthe illumination optics, indicated by 31 b.

FIG. 19 schematically shows another exemplary embodiment of a pupilforming unit according to the disclosure. In this exemplary embodimentan optical conditioning unit 32 c is used to symmetrize an illuminationray bundle at the output of the conditioning unit 32 c without therebyresorting to the polarisation properties of the light for thesymmetrization. A part of the illumination ray bundle is deviated bymirrors 37 a and 37 b. This part of the illumination ray bundle thenpasses through a so-called dove prism 35. The actual mirroring orsymmetrization of the illumination ray bundle takes place inside thedove prism 35, so that at the output of the optical conditioning unit 32c there is an illumination ray bundle which is formed by twoillumination ray sub-bundles mutually symmetrized with respect to anaxis along the propagation direction of the light.

In the exemplary exemplary embodiment according to FIG. 19, it ispossible to dispense with further light mixing with the help of afurther light mixing unit, for example a honeycomb condenser or a rod.Combinations with the other light mixing units, for example thosementioned, are nevertheless possible. Depending on the quality of thelight produced by the light source and forming the illumination raybundle 12, it may be sufficient in the exemplary embodiment according toFIG. 19 to use the symmetrization property of the optical conditioningunit 32 c without additional light mixing to homogenize the illuminationof the multi-mirror array 38.

FIG. 20 schematically shows another exemplary embodiment of an opticalsystem which reduces the effect of the spatial coherence of illuminationray sub-bundles on the intensity distribution produced on themulti-mirror array 38. In contrast to the exemplary embodiment shown inFIG. 8, in which a rotating transparent wedge is used to tilt theillumination ray sub-bundles, the exemplary embodiment shown in FIG. 20uses a mirror, which is capable of performing rotary oscillations, toachieve a similar effect. However, in the exemplary embodiment shown inFIG. 20 the illumination ray sub-beams 121, 122 are tilted only in theplane of the drawing sheet, whereas the bundles 121, 122 shown in FIG. 8perform a rotation around the optical axis. Apart from that, theexemplary embodiment shown in FIG. 20 makes it possible to vary (ifneeded) the maximum tilting angles of the illumination ray sub-bundles,as will become clear from the following description:

The exemplary embodiment shown in FIG. 20 includes a beam splitter plate810 which splits off a small portion of an incident illumination raybundle 12 and directs this portion towards Fourier optics 812. Afterhaving passed the Fourier optics 812, the split off portion impinges ona divergence measurement unit 814 which contains a position resolvingsensor, for example a CCD sensor. The divergence measurement unit 840 isconfigured to measure the divergence of the split off portion of theillumination ray bundle 12.

The remaining portion of the illumination ray bundle 12 passes throughthe beam splitter plate 810 and impinges on a polarization dependentbeam splitting cube 816. The incident illumination ray bundle 12 is in alinear state of polarization which is selected such that the beamsplitting cube 816 completely reflects the illumination ray bundle 12.The reflected bundle 12 passes through a quarter waveplate 818 andimpinges on a plane mirror 820 which can perform rotary oscillationsabout a rotational axis which runs perpendicular to an optical axis 823of the optical system. An actuator 822 is coupled to the mirror 820 andexerts forces on the mirror 820 such that it performs rotaryoscillations, as is indicated by dashed lines and a double arrow in FIG.20. The actuator 822 is connected, via a mirror control unit 824, to thedivergence measurement unit 814. On the opposite side of the beamsplitting cube 816 relay optics 826 are provided that images the mirror820 onto the first channel plate 828 of the honeycomb condenser 32.

In the following the function of the optical system shown in FIG. 20will be explained:

The portion of the illumination ray bundle 12 which has been reflectedby the beam splitting cube 816 impinges on the quarter waveplate 818.There the linear state of polarization is converted into a circularstate of polarization. The circularly polarized light impinges on theoscillating mirror 820 so that, at a given instant, the propagationdirection of the illumination ray bundle 12 is tilted by a degree whichis determined by the instantaneous rotary angle of the mirror 820.

After being reflected from the mirror 820, the illumination ray bundle12 propagates again through the quarter waveplate 818. The circularstate of polarization is then converted back to a linear state ofpolarization which is, however, orthogonal to the linear state ofpolarization of the illumination ray bundle 12 that has been reflectedby the beam splitter cube 816. As a result of this orthogonal state ofpolarization, the illumination ray bundle 12 now passes through the beamsplitting cube 816 and finally impinges, after having passed the relayoptics 826 and the honeycomb condenser 32, on the micro-mirror array 38.

Due to the rotary oscillations of the mirror 820, the illumination raysub-bundles 121, 122 obliquely impinge on the honeycomb condenser 32.The tilt angles, under which the illumination ray bundles impinge on thehoneycomb condenser 32, periodically vary in time with a period which isdetermined by the period of the rotary oscillations of the mirror 820.In FIG. 20 this continuous tilting of the illumination ray sub-bundlesis illustrated for the illumination ray sub-bundle 121 in solid anddashed lines.

The effect of this continuously oscillating tilting of the illuminationray sub-bundles 121 will now be explained in more detail with referenceto FIGS. 21, 22 and 23 which show the illumination ray sub-bundle 121,which has a small divergence and on the honeycomb condenser 32, at threedifferent instants. As can be seen in FIG. 21, the illumination raysub-bundle 121, which completely illuminates a channel of the firstchannel plate 828 of the honeycomb condenser 32, converges towards thecorresponding channel of the second channel plate 830. At the instantshown in FIG. 21, only a lower portion of a light entrance surface 832of this channel of the second channel plate 830 is illuminated by theillumination ray sub-bundle 121.

At a later instant shown in FIG. 22 the illumination ray sub-bundle 121is tilted by the mirror 820 such that it propagates parallel to theoptical axis 823. Now a central portion of the corresponding channel ofthe second channel plate 830 is illuminated by the convergingillumination ray sub-bundle 821.

At a still later instant the illumination ray sub-bundle 121 is tiltedsuch that an upper portion of the corresponding channel of the secondchannel plate 830 is illuminated, see FIG. 23. From this it becomesclear that it is possible to (almost) homogeneously illuminate the lightentrance surface 832 of the second channel plate 830 by suitablyselecting the maximum amplitude of the rotary oscillations of the mirror830. This is advantageous because the transparent material, from whichthe second channel plate 830 is made, may be damaged if the lightintensities are too large. Such large light intensities may occur if theillumination ray sub-bundles 121 are focused by the channels of thefirst channel plate 828 such that the focal points lie within thechannels of the second channel plate 830.

If the divergence of the illumination ray sub-bundle 121 does not varyduring time, the focal length of the channels of the first channel plate828 may be determined such that the focal points do not lie within thechannels of the second channel plate 830. However, under usualcircumstances variations of the divergence of the illumination raysub-bundles 121 cannot be completely prevented. Under such conditions itis possible that the divergence changes to an extent that leads tountolerable intensities in the second channel plate.

The optical system shown in FIG. 20 prevents such damages by spatiallyvarying the areas which are illuminated on the light entrance surfaces832 of the channels of the second channel plate 830.

In order to avoid that, as a result of changes of the divergence of theillumination ray sub-bundles 121, the illuminated areas on the channelsof the second channel plate 830 become too small, or that these areasextend to adjacent channels which is desirably avoided, too, the opticalsystem measures the divergence of the incoming illumination ray bundle12 via the divergence measurement unit 814. The measurement values arecommunicated to the mirror control unit 824 which controls the maximumamplitudes of the rotary oscillations produced by the actuator 822 insuch a manner that the conditions shown in FIGS. 21, to 23 prevail, i.e.the light entrance surfaces 832 of the second channel plate 830are—although not at any arbitrary instant, but integrally overtime—completely illuminated, or at least illuminated over an area thatprevents damages caused by too high light intensities.

In the following, some additional exemplary embodiments will bedescribed:

If the divergence is known, or its variations are within known ranges,the beam splitter plate 810, the Fourier optics 812 and the divergencemeasurement unit 814 may be dispensed with.

In another exemplary embodiment, the mirror 820 does not perform rotaryoscillations. but is bent with the help of suitable actuators, with abending axis extending perpendicular to the plane of the drawing sheet.

In another alternative exemplary embodiment the beam splitting cube 816and the quarter waveplate 818 are dispensed with. The mirror 820 isarranged such that its surface normal (in neutral position) forms anangle with regard to the direction of the incoming illumination raybundle 12. In other words, the mirror 820 is then used as a foldingmirror. As a result of this inclined orientation, the honeycombcondenser 32 may be arranged in an inclined manner as well, inparticular in accordance with the Scheimpflug condition.

In still another exemplary embodiment the relay optics 826 are dispensedwith. However, in this case not only the angles of incidence, but alsothe areas, where the illumination ray sub-bundles 121 impinge on thefirst channel plate 828, will vary in time. If this can be tolerated,the omission of the relay optics 826 significantly simplifies the designof the optical system.

In another alternative exemplary embodiment the quarter waveplate 818 isreplaced by another polarization manipulator, for example a polarizationrotator that rotates the polarization direction by an angle of 45°. Sucha polarization rotator may include optically active materials, forexample.

FIG. 24 schematically shows a section through a mixing element 903 whichmay be used instead of the diffractive optical element 3 d in thearrangement shown in FIG. 11. The mixing element 903 includes a firstrod 910 and a second rod 912 which are transparent for the illuminationray bundles. The first rod 910 has a first surface 914, and the secondrod 912 has a second surface 916 which is arranged adjacent the firstsurface 914 of the first rod 910. The first surface 914 and the secondsurface 916 are parallel to each other and are spaced apart by adistance D which is so small that at least a substantial portion oflight guided by total internal reflection within the first rod 910couples into the second rod 912 as evanescent waves.

Such evanescent waves are a side effect if total internal reflectionoccurs. The evanescent waves propagate across the boundary surfacebetween the two adjoining optical media. Under ordinary conditionsevanescent waves do not transmit any energy. However, if the distancebetween the two media is less than several wavelengths, i.e. there is athin interspace filled with a third medium, the evanescent wave transferenergy across the interspace into the second medium across the thirdmedium. The smaller the distance is, the larger is the fraction of lightwhich couples into the second medium. This effect, which is very similarto quantum tunnelling, is also referred to as frustrated total internalreflection.

In order to be able to keep the distance D between the first and secondsurfaces 914, 916 smaller than a few wavelengths of the light, thesurfaces 914, 916 are desirably plane because this simplifies a parallelarrangement of the surfaces 914, 916 with such a short distance D. Inthe exemplary embodiment shown the distance D is determined by spacers918 which are arranged between the surfaces 914, 916. The spacers 918may be formed by stripes of a thin film, for example a gold film, orsputtered structures. The rods may have almost any cross section, forexample rectangular with an aspect ratio such that the rod has the shapeof a thin slab.

Reference numeral 920 denotes a centroid ray of an illuminationsub-bundle. If this ray 920 is coupled into a front end face 921 of therod 910 with a suitable angle of incidence, it can be ensured that theangle of incidence on its lateral surface 923 is greater than thecritical angle, so that total internal reflection occurs at this lateralsurface 923.

If the ray 920 reflected from lateral surface 923 is incident on thefirst surface 914, a fraction of the light is able to couple into theadjoining second rod 912 so that a beam splitting function is achieved.A reflected portion is directed again towards the lateral surface 923,and the transmitted portion impinges on the lateral surface 925 of thesecond rod 912. Each time a ray impinges on one of the first or secondsurfaces 914, 916 it will be split into two rays in this manner.

From the opposite rear end faces 927, 929 of the rods 910, 912 aplurality of rays emerge that carry a fraction of the intensity of theray 920 before it is coupled into the rod 910. The fraction depends onthe geometrical parameters of the mixing element 903, in particular onthe distance D, the angle of incidence on the front end face 921 and thelength and thickness of the rods 910, 912.

If a larger portion of the front end face 921 of the mixing element 903is illuminated with an illumination ray bundle, a very effective lightmixing effect is achieved with a mixing element 903 having a shortlongitudinal dimension. One of the most prominent advantages of thisexemplary embodiment is that no light is lost at the optical boundaries.The only light loss occurs as a result of light absorption within therods 910, 912 which can be kept very low if highly transparent opticalmedia are used.

In order to reduce polarization dependencies, the light bundlespropagating through the mixing elements 903 is desirably in an s-stateof linear polarization.

In one exemplary embodiment the illumination ray bundle has a wavelengthof 193 nm, the angle of incidence with respect to the first and secondsurfaces 914, 916 is 45°, and the distance D is 100 nm, i.e. about onehalf of the light wavelength. This will result in a beam splitting ratioof about 50:50 at the surfaces 914, 916. Rods having the desiredflatness and minimum roughness are commercially available, for example,from Swissoptic, Switzerland.

FIG. 25 is a schematic cross-section through a mixing unit 950 whichincludes a plurality of mixing elements 903 as shown in FIG. 24. Themixing elements 903 in this exemplary embodiment have a thickness in theorder of 1 mm to 2 mm and a length between 10 mm and 50 mm and mayconsist of calcium fluoride, magnesium fluoride, quartz or fused silica.The thicknesses of the mixing element 903 do not have to be equal.

A prism 952 is arranged behind the rear end faces of the mixing elements903. The prism 952 tilts the ray bundles emerging from the rear endfaces under various directions such that the ray bundles run parallel.To this end the prism 952 has two inclined end faces whose inclinationis adapted to the angles and which the ray bundles emerge from themixing elements 903. Instead of the prism 952 a suitable mirrorarrangement may be used, as is known in the art as such.

The intensity distributions exemplarily illustrated at the bottom ofFIG. 25 show the inhomogeneities of the intensity distribution of theillumination ray bundle before and after the mixing unit 950.

Since the ray bundles emerge from the rear end faces of the mixingelements 903 under two opposite angles, it may be envisaged toilluminate the front end faces of the mixing elements 903 under the twoopposite angles, too. This further improves the light mixing effectobtained by the mixing unit 950. In order to facilitate the coupling oflight into the front end faces of the mixing elements 903, these endfaces may have the shape of prisms, as is indicated for the upper mostmixing element 903 in FIG. 25 by a dotted line 954.

In another alternative exemplary embodiment a plurality of mixing units(but without the prism 950) are arranged one behind the other in acascaded fashion so that light emerging from a rear end face of a unitcouples into a front end face of a subsequent unit. The prism 950 may bearranged behind the last units of the cascade.

FIG. 26 is a schematic cross-section through a light mixing elementaccording to still another exemplary embodiment. Like elements as shownin FIG. 24 are denoted with the same reference numerals increased by100. The light mixing element 1003 differs from the light mixing element903 shown in FIG. 24 mainly in that the interspace formed between thefirst and second surface 1014, 1016 is not filled by air or another gas(mixture), but by a dielectric material, for example highly purifiedwater or a dielectric beam splitting layer including a plurality ofindividual sub-layers. Then it is not necessary to keep the distance Dbetween the surfaces 1014, 1016 in the order of some tenth or severalhundreds of nanometers, or generally at a distance at which frustratedinternal reflection occurs. This simplifies the production and mountingof the rods 1010, 1012.

Since the dielectric medium arranged in the interspace between thesurfaces 1014, 1016 usually has a higher absorption for the illuminationray bundle than the material of the rods 1010, 1012, the optical lossesin the light mixing element 1003 may be somewhat higher than in theexemplary embodiment shown in FIG. 24.

As a matter of course, the light mixing elements 1003 may also be usedin a mixing unit 950 as has been shown in FIG. 25.

FIG. 27 is a schematic cross-section through a light mixing element 1103according to a still further exemplary embodiment. The light mixingelement 1103 includes a slab 1114 which has (integrally or formed on) aprism portion 1116 with an inclined front end face 1118. If anillumination ray sub-bundle represented by a centroid ray 1120 iscoupled into the slab 1114 via its front end face 1118, it will travelto and fro within the slab 1114 due to total internal reflection at itssurfaces. However, the angle of incidence of the ray 1120 on theparallel lateral surfaces 1122, 1124 of the slab 1114 is determined suchthat the angle of incidence is only close to the critical angle. Thus ateach reflection at one of the surfaces 1122, 1124 a portion of the ray1120 is transmitted and emerges from the slab 1114 as refracted ray1120′. The fraction of light which is transmitted at the surfaces 1122,1124 is determined by the angle of incidence and the refractive indicesof the slab 1114 and the surrounding medium (usually air or anothergas). The function of the slab 1114 is therefore similar to the functionof a Lummer-Gehrke plate which is used as a spectroscope in the field ofoptics.

Also in this exemplary embodiment the refracted rays 1120′ emerge fromthe slab 1114 under two different angles. In order to obtain ray bundlesrunning parallel, prisms 1112 a, 1112 b and mirrors 1113 a, 1113 b areused.

In contrast to the Lummer-Gehrke plate, it is desirably avoided that therefracted bundles 1120′ produce interference patterns in the far field.This can be ensured if the distance a between two reflections within theslab 1114 is in the order of the temporal coherence length of the light.For light having a wavelength of 193 nm and a bandwidth of 1.5 pm, a=2.5cm. Incidentally, the same condition also applies to the exemplaryembodiments shown in FIGS. 24 to 26.

The pupil forming unit according to the disclosure of FIGS. 3, 9 and 10,the optical system according to the disclosure of FIGS. 4 to 8 and 16 to24, and the optical conditioning unit according to the disclosure ofFIGS. 11 to 14 provide a temporal stabilisation of the illumination ofthe multi-mirror array (MMA) 38 of illumination optics for a projectionexposure apparatus for microlithography by the superposition ofillumination ray sub-bundles.

These various exemplary embodiments therefore show illumination opticsaccording to the disclosure for a projection exposure apparatus formicrolithography for the homogeneous illumination of an object fieldwith object field points in an object plane. The illumination opticshave an associated exit pupil for each object field point of the objectfield. The illumination optics contain at least one multi-mirror array(MMA) having a multiplicity of mirrors for adjusting an intensitydistribution in the associated exit pupils of the object field points.The illumination optics have an illumination ray bundle of illuminationrays between a light source and the multi-mirror array (MMA). Theillumination optics contain at least one optical system for temporallystabilising illumination of the multi-mirror array (MMA), where thetemporal stabilisation is carried out by superposition of illuminationrays of the illumination ray bundle on the multi-mirror array (MMA).

It is desirable to stabilise the illumination of the multi-mirror array(MMA) in order to decouple this illumination, and therefore the exitpupils of the object field points, of a projection exposure apparatusfrom the temporal and/or spatial fluctuations of a light source.

By this decoupling, it is possible for the intensity distribution in theexit pupils of object field points, produced by a projection exposureapparatus having the pupil forming unit according to the disclosure ofFIGS. 3, 9 and 10, the optical system according to the disclosure ofFIGS. 4 to 8 and 16 to 27, and the optical conditioning unit accordingto the disclosure of FIGS. 11 to 14, to deviate only slightly from adesired intensity distribution in respect of the centroid angle value,the ellipticity and the pole balance.

These exemplary embodiments show a projection exposure according to thedisclosure apparatus for microlithography having illumination optics forilluminating an object field with object field points in an objectplane, and projection optics for imaging the object field into an imagefield in the image plane. The illumination optics have, for each objectfield point of the object field, an associated exit pupil with agreatest marginal angle value sin(γ) of the exit pupil. The illuminationoptics contain at least one multi-mirror array (MMA) having amultiplicity of mirrors for adjusting an intensity distribution in theassociated exit pupils of the object field points. The illuminationoptics contain at least one optical system for temporally stabilisingillumination of the multi-mirror array (MMA) so that, for each objectfield point, the intensity distribution in the associated exit pupildeviates from a desired intensity distribution in the associated exitpupil:

-   -   in the case of a centroid angle value sin(β) by less than two        percent expressed in terms of the greatest marginal angle value        sin(γ) of the associated exit pupil; and/or    -   in the case of ellipticity by less than two percent; and/or    -   in the case of a pole balance by less than two percent.

By this decoupling it is likewise possible for a first intensitydistribution, produced in the exit pupils of object field points by aprojection exposure apparatus according to the disclosure, to deviateonly slightly in the outer σ or inner σ from a second intensitydistribution being produced.

The exemplary embodiments mentioned above therefore likewise show aprojection exposure apparatus according to the disclosure formicrolithography, having illumination optics for illuminating an objectfield with object field points in an object plane,

having projection optics for imaging the object field into an imagefield in the image plane,the illumination optics having, for each object field point of theobject field, an associated exit pupil with a greatest marginal anglevalue sin(γ) of the exit pupil,the illumination optics containing at least one multi-mirror array (MMA)having a multiplicity of mirrors for adjusting an intensity distributionin the associated exit pupils of the object field points,the illumination optics containing at least one optical system fortemporally stabilising the illumination of the multi-mirror array (MMA),so that for each object field point, a first adjusted intensitydistribution in the associated exit plane deviates from a secondadjusted intensity distribution in the associated exit pupil by lessthan the value 0.1 in the outer and/or inner α.

The multi-mirror array (MMA) 38 according to the disclosure of FIGS. 3to 12, 14 and 16 to 27 is configured according to the considerationspresented above in the introduction to the description, in order tosatisfy the properties of a desired resolution in the pupil for a changebetween annular settings, which differ only slightly in the outer and/orinner α. Furthermore the multi-mirror array 38 according to thedisclosure in the exemplary embodiments of the figures shown inter aliasatisfies the properties for the installation space of a projectionexposure apparatus and the property of a minimum size of the pupil inthe pupil plane 44.

The exemplary embodiments therefore show a multi-mirror array (MMA) forillumination optics for a projection exposure apparatus formicrolithography, having an operating light wavelength λ of theprojection exposure apparatus in the units [nm],

each mirror of the multi-mirror array being rotatable about at least oneaxis through a maximum tilt angle value sin(α) and having a minimum edgelength, the minimum edge length being greater than 200 [mm*nm]*sin(α)/λ.

The optical system according to the disclosure of FIGS. 4 to 8 and 16 to27 ensures homogenisation of this illumination, extending beyond puretemporal stabilisation of the illumination of the multi-mirror array(MMA) 38, by the superposition of illumination ray sub-bundles on themulti-mirror array. In this case the optical system according to thedisclosure in the exemplary embodiments, for the reasons mentioned abovein the introduction to the description, introduce only little additionalgeometrical flux in the form of an increased divergence of theillumination ray sub-bundles after the optical system according to thedisclosure.

The exemplary embodiments therefore show an optical system according tothe disclosure for homogenising illumination of a multi-mirror array ofillumination optics for a projection exposure apparatus formicrolithography, having a divergence of the illumination ray bundle andan illumination light direction from the light source to themulti-mirror array (MMA), the divergence of the illumination ray bundlein the illumination light direction after the optical system being lessthan five times the divergence of the illumination ray bundle before theoptical system.

The optical conditioning unit according to the disclosure of FIGS. 11 to15 is capable of modifying the position, the divergence and/or the rayor bundle profile and/or the polarisation state of the illumination raybundle 12 between the laser output from a laser 110 and the multi-mirrorarray (MMA) 38.

The exemplary embodiments therefore show an optical conditioning unitaccording to the disclosure for conditioning an illumination ray bundleof a laser for illumination optics for a projection exposure apparatusfor microlithography, the laser having more than one coherent laser modeand a laser output, and the illumination ray bundle having a divergence,a ray or bundle profile and a polarisation state, the opticalconditioning unit modifying at least the divergence and/or the ray orbundle profile and/or the polarisation state of the illumination raybundle between the laser output and the multi-mirror array (MMA).

The present disclosure is not restricted to the exemplary embodimentsnoted above.

Such exemplary embodiments as result from a combination of features ofindividual embodiments which fall within the patent claims, or which arepresented in the exemplary embodiments described above, are alsoconsidered to be covered by the disclosure.

An example which may be mentioned is the combination of the embodimentsaccording to FIGS. 16 and 17, in which case the integrators 32 and 32 amay also be operated in common by sequential arrangement in the lightpropagation direction. Also to be indicated by way of example are themany combination possibilities of the conditioning unit 400 which wasdescribed by way of example in connection with FIGS. 12 to 14, with anintegrated 32 or 32 a, in which case the two units may be arrangedsuccessively in the illumination ray bundle in any desired sequence inthe light direction before the multi-mirror array 38.

Furthermore, besides the embodiments which result from combiningfeatures of individual embodiments described above, embodimentsaccording to the disclosure which are likewise considered to be coveredby the disclosure may also be obtained by interchanging features fromdifferent embodiments.

1.-58. (canceled)
 59. An apparatus, comprising: illumination opticsconfigured to illuminate object field points of an object field in anobject plane; and projection optics configured to image the object fieldon an image field in an image plane, wherein: the illumination opticshave, for each object field point of the object field, an exit pupilassociated with the object point; the illumination optics comprise amulti-mirror array comprising a plurality of mirrors configured toadjust an intensity distribution in exit pupils associated to the objectfield points; the illumination optics comprise an optical systemconfigured to temporally stabilise the illumination of the multi-mirrorarray by superposing the illumination rays of the illumination raybundle on the multi-mirror array; the optical system is configured forspatially homogeneous illumination of the multi-mirror array; and theapparatus is a microlithography projection exposure apparatus.
 60. Theapparatus of claim 59, wherein the apparatus has an operating lightwavelength λ in units [nm], each mirror of the multi-mirror array isrotatable about at least one axis through a maximum tilt angle valuesin(α), and each mirror of the multi-mirror array has a minimum edgelength which is greater than 200 [mm*nm]*sin(α)/λ.
 61. The apparatus ofclaim 60, wherein the object field has an illuminated object fieldsurface having a size OF, and an illuminated surface of the multi-mirrorarray has a size AF, where AF=c*sin(γ′)/sin(α)*OF, c is a constant with0.1<c<1, and sin(γ′) is a greatest marginal angle value among greatestmarginal angle values sin(γ) associated with the exit pupils of theobject field points.
 62. The apparatus of claim 59, wherein an averagereflectivity of the mirrors of the multi-mirror array for an angle ofincidence between 0° and 60° is more than 25%.
 63. The apparatus ofclaim 62, wherein a standard deviation of the reflectivity of themirrors of the multi-mirror array from the average reflectivity is, foran angle of incidence between 0° and 60°, less than 50% expressed interms of the average reflectivity.
 64. The apparatus of claim 59,wherein the apparatus is a scanner, and the intensity distribution ofthe exit pupils of the object field points are modified when theapparatus is used during the scan process.
 65. The apparatus of claim59, wherein an illuminated solid angle range in the exit pupilassociated with an object field point, which range is generated by amirror of the multi-mirror array, has a maximum angle range value whichis less than 5% expressed in terms of a greatest marginal angle valuesin(γ) of the associated exit pupil.
 66. The apparatus of claim 59,wherein a solid angle range in the exit pupil associated with an objectfield point is illuminated with a non-zero intensity and an angle rangevalue of less than 10% expressed in terms of the greatest marginal anglevalue of the associated exit pupil by at least two mirrors of themulti-mirror array.
 67. The apparatus of claim 59, wherein a greatestmarginal angle value sin(γ) of the exit pupil associated with an objectfield point is greater than 0.2 for all object field points.
 68. Theapparatus of claim 59, wherein the illumination ray bundle has adivergence and an illumination light direction from the light source tothe multi-mirror array, and the divergence of the illumination raybundle in the illumination light direction after the optical system isless than twice the divergence of the illumination ray bundle before theoptical system.
 69. The apparatus of claim 59, wherein the opticalsystem has a telescopic beam path which is folded by at least one prismor a mirror.
 70. The apparatus of claim 59, wherein the optical systemis configured to produce an incoherent superposition of the illuminationrays of the illumination ray bundle on the multi-mirror array.
 71. Theapparatus of claim 59, wherein, during use, the apparatus hasillumination rays of an illumination ray bundle between a light sourceand the multi-mirror array, the mirrors of the multi-mirror array havemirror surfaces, and the optical system comprises at least one opticaldevice configured to concentrate illumination rays of the illuminationray bundle on the mirror surfaces of the mirrors of the multi-mirrorarray.
 72. The apparatus of claim 59, further comprising a laserconfigured to generate an illumination ray bundle, wherein: the laserhas more than one coherent laser mode and a laser output; theillumination ray bundle has a divergence, a ray or bundle profile and apolarisation state; the optical system comprises an optical conditioningunit configured to modify at least one parameter selected from the groupconsisting of the divergence of the illumination ray bundle between theoutput of the laser and the multi-mirror array, the ray profile of theillumination ray bundle between the output of the laser and themulti-mirror array, and the polarisation state of the illumination raybundle between the output of the laser and the multi-mirror array. 73.The apparatus of claim 59, wherein at least one mirror of themulti-mirror array has a different surface content than another mirrorof the multi-mirror array.
 74. The apparatus of claim 59, wherein atleast one mirror of the multi-mirror array has a different shortestdistance from its closest neighbouring mirror than another mirror of themulti-mirror array.
 75. The apparatus of claim 59, wherein theillumination optics comprise at least two multi-mirror arrays, the atleast two multi-mirror arrays differing from each other in at least oneproperty of a mirror.
 76. The apparatus of claim 59, wherein the opticalsystem comprises: a mirror having a mirror surface; and an actuatorconfigured to produce a tilt of at least a portion of the mirrorsurface.
 77. The apparatus of claim 76, wherein the optical system isconfigured to produce a temporal modification of the incoherentsuperposition.
 78. The apparatus of claim 76, wherein the optical systemis between a light source and the multi-mirror array, wherein anillumination ray of the illumination ray bundle has a height withrespect to an optical axis in a plane between the light source and themulti-mirror array perpendicularly to the optical axis, and the opticalsystem comprises an optical phase element configured to introduce aphase lag of the illumination ray as a function of the height of theillumination ray with respect to the optical axis.
 79. The apparatus ofclaim 78, wherein the optical system comprises a honeycomb condenserhaving a first honeycomb channel plate and a second honeycomb channelplate arranged in a focal plane of the first honeycomb channel plate,and the optical phase element is arranged between the first and thesecond honeycomb channel plate.
 80. The apparatus of claim 78, whereinthe optical phase element modifies a phase of the illumination raybundle in a spatially periodic manner.
 81. The apparatus of claim 79,wherein the honeycomb condenser has a focal length of more than 5 m. 82.An apparatus, comprising: illumination optics configured to illuminateobject field points of an object field in an object plane, theillumination optics comprising: a multi-mirror array comprising aplurality of mirrors; at least one optical system configured totemporally stabilise the illumination of the multi-mirror array, the atleast one optical system comprising: a honeycomb condenser having afirst honeycomb channel plate and a second honeycomb channel platearranged in a focal plane of the first honeycomb channel plate, and anoptical phase element arranged between the first and the secondhoneycomb channel plates; and projection optics configured to image theobject field of the illumination optics on an image field in an imageplane, wherein: the illumination optics have, for each object fieldpoint of the object field, an exit pupil associated with the objectpoint; the multi-mirror array is configured to adjust an intensitydistribution in exit pupils associated to the object field points; andthe apparatus is a microlithography projection exposure apparatus.